Update "The Hard Way" setup for Arch Linux

MariaDB cannot be started on Arch Linux before running a command to create the database files

See https://wiki.archlinux.org/index.php/MariaDB#Installation

It also appears that memcached is not started by default on Arch Linux,
so it has been added to the systemctl startup step.

This PR adds that step when setting up on Arch Linux

Pass env_name as a string in test databases

In 154abcab we switched from using `Rails.env` to fetch the `env_name` to
`ActiveRecord::ConnectionHandling::DEFAULT_ENV.call.to_sym` which
changed the type from a `String` to a `Symbol`.

This commit brings things back to the original state, so we can find the
configurations correctly!

It also modifies the configuration in the configurations array, so that
future connections can find the database with the updated keyword value.

When all IPs are trusted, use the furthest away

Fix regression where AJ#perform_now doesn't return the job's value:

- I made a change in 0d3aec49 to output a log if a job was aborted
  in a before callbacks. I didn't take in consideration that a job
  could return a falsy value and thus it would wrongly log
  that the job was aborted.

  This fixes the problem by checking if the callback chain was halted
  rather than the return value of the job.

- Fix #38040

Scenario: we have a REMOTE_ADDR of `127.0.0.1`, and X-Forwarded-For is
`A, B, C`.

Without any relevant trust, the `remote_ip` is `C`.

If `C` is trusted, then the `remote_ip` is `B`.

If `B` and `C` are trusted, then the `remote_ip` is `A`.

If all of `A`, `B`, and `C` are trusted, then the `remote_ip` should
still be `A`: if our trust was sufficient to get that far out before,
trusting something else should not have us fall back to `127.0.0.1`.

It is this last situation that we're correcting here:

We trust `A` to give us accurate X-Forwarded-For information, yet it has
chosen to leave it unset. Therefore, `A` is telling us that it is itself
the client.

Fix regression, enforce fresh ETag header after collection contents change

Add ActiveRecord::Relation#cache_key_with_version. This method will be
used by ActionController::ConditionalGet to ensure that when collection
cache versioning is enabled, requests using ConditionalGet don't return
the same ETag header after a collection is modified.

Prior to the introduction of collection cache versioning in
4f2ac80d, all collection cache keys
included a version. However, with cache versioning enabled, collection
cache keys remain constant. In turn, ETag headers remain constant,
rendering them ineffective.

This commit takes the cache_key_with_version method used for individual
Active Record objects (from aa8749eb),
and adds it to collections.

Add `ActionDispatch::HostAuthorization` to "Configuring Middleware" guide [ci skip]

Add to the log format "*/*" if using a not found format:

Separate with space between table name and columns list in SQL of insert_all

Mime::Mimes#symbols should return a always up to date reference:

The rendering template is processing as */* but in the log is
  "Processing by Controller#action as "

This change add the */* for the log and showing as
  "Processing by Controller#action as */*"
when there not founds for the extension of format.

- Original issue was reported in https://github.com/rails/rails/issues/38094
  and a fix attempted in https://github.com/rails/rails/pull/38126 but
  it's not the proper fix I think.

  TL;DR Is that `ActionView::Base.default_formats` holds a copy of
  mime symbols at the time ActionView::Base is loaded.
  So if you try to register mime types after ActionView Base is loaded
  then it won't work.

  ```ruby
    ActionView::Base.default_formats ||= Mime::SET.symbols # Note that this is automatically done when ActionView get loaded https://github.com/rails/rails/blob/22483b86a6c779743b30e2f23bb46accfbf96b28/actionpack/lib/action_dispatch.rb#L117

   Mime::Type.register_alias "application/xhtml+xml", :foobar
   puts ActionView::base.defaults_formats.include?(:foobar) # => false
  ```

  Same issue if you try to unregister a mime after ActionView is loaded.
  That's what was happening in the flaky test:

  ```
   Mime::Type.register_alias "application/xhtml+xml", :foobar
   ActionView::Base.default_formats ||= Mime::SET.symbols

   puts ActionView::base.defaults_formats.include?(:foobar) # => true

   Mime::Type.unregister(:foobar)
   puts ActionView::base.defaults_formats.include?(:foobar) # => true
  ```

  ### Solution

  Return a refence to `@symbols` which is updated each time a new mime is
  registered/unregistered.

This commit copies info from
https://github.com/rails/rails/pull/33145
([an excellent changelog](https://github.com/rails/rails/blob/6-0-stable/railties/CHANGELOG.md)) to
our guides.

Closes https://github.com/rails/rails/issues/36959
Not sure whether there is a need mentioning `config.hosts` in the "Upgrading to Rails 6.0" guide
since it is configured to work in the development environment by default and we guide how to deal
with "blocked host" issue, see:
https://github.com/rails/rails/blob/6-0-stable/actionpack/lib/action_dispatch/middleware/templates/rescues/blocked_host.html.erb

I would like to backport this to `6-0-stable` so users will be able to
find info about `ActionDispatch::HostAuthorization` middleware and how
to configure it.

Give credit to @gsamokovarov since I copied the info from the changelog. <3

[bogdanvlviv, Genadi Samokovarov]

Closes #38132

In arel, there is a space between the table name and columns list when INSERT.
https://github.com/rails/rails/blob/3c28e79b615f6937f5abdc433ff634d15cf2466f/activerecord/lib/arel/visitors/to_sql.rb#L56

```ruby
User.create!(name: "foo")
# INSERT INTO `users` (`name`) VALUES ('foo')
              ^^^^^^^^^^^^^^^^
```

But SQL of insert_all is not separated.

```ruby
User.insert_all!([{name: "foo"}])
# INSERT INTO `users`(`name`) VALUES ('foo')
              ^^^^^^^^^^^^^^^
```

This is not a problem (because it is correct as SQL), but fixing this will make unified behavior.

A known issue is that database_rewinder fails to parse table name on insert_all.
https://github.com/amatsuda/database_rewinder/blob/v0.9.1/lib/database_rewinder.rb#L51-L54

```ruby
statement = "INSERT INTO `users`(`name`) VALUES ('foo')"
match = statement.match(/\A\s*INSERT(?:\s+IGNORE)?(?:\s+INTO)?\s+(?:\.*[`"]?([^.\s`"]+)[`"]?)*/i)
# => #<MatchData "INSERT INTO `users`(`name`)" 1:")">
# Expected behavior is
# => #<MatchData "INSERT INTO `users`" 1:"users">
```

Use travel_to to in date_helper_test.rb.

Remove Travis CI files

Rails CI has been running at Buildkite for 9 month.
Refer https://github.com/rails/rails/commit/e485c14a3ee29ee486324a96545abf964d428101

Rather than replace `ENV['TRAVIS']` with `ENV['CI']`, I think we can
remove this condition because `ENV['TRAVIS']` is not valid at Buildkite
then Rails CI has been running with `PROCESS_COUNT` about 9 month
since this https://github.com/rails/rails/commit/e485c14a3ee29ee486324a96545abf964d428101

Address StarStarMimeControllerTest#test_javascript_with_no_format_only_star_star failure

Add ActionCable subscription connection identifier to PostgreSQL adapter

* The last html block wasn't formatting properly, it needed a blank line
  between the paragraph and the text.
* The ordered list wasn't generating the sequence, but always showing 1.,
  the inner content/examples needed to be indented for that to work.
* Mark some pieces as inline code for highlighting.
* Tweak a couple sentences.

  * You can distinguish connection among others with specific `application_name`

    ```sql
    SELECT application_name FROM pg_stat_activity;
    /*
        application_name
    ------------------------
    psql
    ActionCable-PID-42
    (2 rows)
    */
     ```

  * It's possible to customize connection identification with `id` option in `cable.yml`

    `ActionCable-PID-#{$$}` is the default value

  * Related tests refactoring

  * `ActionCable::Server#config.cable` is no mutated anymore inside Redis subscription adapter

Fix #38094

* Steps to reproduce:

```ruby
% cd actionpack
% MT_CPU=0 bundle exec ruby -w -Itest test/controller/mime/accept_format_test.rb -n "/^(?:MimeControllerLayoutsTest#(?:test_missing_layout_renders_properly)|StarStarMimeControllerTest#(?:test_javascript_with_no_format_only_star_star))$/" --verbose --seed 15759
```

* Actual result without this commit:

```ruby
% cd actionpack
% MT_CPU=0 bundle exec ruby -w -Itest test/controller/mime/accept_format_test.rb -n "/^(?:MimeControllerLayoutsTest#(?:test_missing_layout_renders_properly)|StarStarMimeControllerTest#(?:test_javascript_with_no_format_only_star_star))$/" --verbose --seed 15759
Run options: -n "/^(?:MimeControllerLayoutsTest#(?:test_missing_layout_renders_properly)|StarStarMimeControllerTest#(?:test_javascript_with_no_format_only_star_star))$/" --verbose --seed 15759

MimeControllerLayoutsTest#test_missing_layout_renders_properly = 0.18 s = .
StarStarMimeControllerTest#test_javascript_with_no_format_only_star_star = 0.00 s = E

Error:
StarStarMimeControllerTest#test_javascript_with_no_format_only_star_star:
ArgumentError: Invalid formats: :iphone
    /Users/yahonda/src/github.com/yahonda/rails/actionview/lib/action_view/lookup_context.rb:287:in `formats='
    /Users/yahonda/src/github.com/yahonda/rails/actionview/lib/action_view/view_paths.rb:11:in `formats='
    /Users/yahonda/src/github.com/yahonda/rails/actionpack/lib/action_controller/metal/rendering.rb:29:in `process_action'
    /Users/yahonda/src/github.com/yahonda/rails/actionpack/lib/abstract_controller/callbacks.rb:42:in `block in process_action'
    /Users/yahonda/src/github.com/yahonda/rails/activesupport/lib/active_support/callbacks.rb:98:in `run_callbacks'
    /Users/yahonda/src/github.com/yahonda/rails/actionpack/lib/abstract_controller/callbacks.rb:41:in `process_action'
    /Users/yahonda/src/github.com/yahonda/rails/actionpack/lib/action_controller/metal/rescue.rb:22:in `process_action'
    /Users/yahonda/src/github.com/yahonda/rails/actionpack/lib/action_controller/metal/instrumentation.rb:34:in `block in process_action'
    /Users/yahonda/src/github.com/yahonda/rails/activesupport/lib/active_support/notifications.rb:203:in `block in instrument'
    /Users/yahonda/src/github.com/yahonda/rails/activesupport/lib/active_support/notifications/instrumenter.rb:24:in `instrument'
    /Users/yahonda/src/github.com/yahonda/rails/activesupport/lib/active_support/notifications.rb:203:in `instrument'
    /Users/yahonda/src/github.com/yahonda/rails/actionpack/lib/action_controller/metal/instrumentation.rb:33:in `process_action'
    /Users/yahonda/src/github.com/yahonda/rails/actionpack/lib/action_controller/metal/params_wrapper.rb:245:in `process_action'
    /Users/yahonda/src/github.com/yahonda/rails/actionpack/lib/abstract_controller/base.rb:136:in `process'
    /Users/yahonda/src/github.com/yahonda/rails/actionview/lib/action_view/rendering.rb:39:in `process'
    /Users/yahonda/src/github.com/yahonda/rails/actionpack/lib/action_controller/metal.rb:190:in `dispatch'
    /Users/yahonda/src/github.com/yahonda/rails/actionpack/lib/action_controller/test_case.rb:512:in `process'
    /Users/yahonda/src/github.com/yahonda/rails/actionpack/lib/action_controller/test_case.rb:390:in `get'
    test/controller/mime/accept_format_test.rb:28:in `test_javascript_with_no_format_only_star_star'

rails test test/controller/mime/accept_format_test.rb:26

Finished in 0.180610s, 11.0736 runs/s, 11.0736 assertions/s.
2 runs, 2 assertions, 0 failures, 1 errors, 0 skips
%
```

* How to diagnose this error:

At first Restore `require "action_view/base"` to `actionpack/lib/action_dispatch/middleware/debug_exceptions.rb` addresses this error,
then isolated which lines are required then found this line is required.

https://github.com/rails/rails/blob/22483b86a6c779743b30e2f23bb46accfbf96b28/actionpack/lib/action_dispatch.rb#L117

```ruby
  ActionView::Base.default_formats ||= Mime::SET.symbols
```

Set AJ `return_false_on_aborted_enqueue` true in the test suite:

Return unfrozen strings from to_sentence

Do not abort `rails new` when git binary doesn't exist