Add unpermitted_parameters hook to instrumentation guide [ci skip]

Fix test name for daemon option test

In this test file, "server option" refers to the server used to start
Rails(e.g. `puma`, `thin`).
But this test, "server option" is not specified. Therefore, I think that
it is incorrect that `server_option` is included in the test name.

Remove unsued `jquery-rails`

Use __dir__  in activestorage/

Added test case for starting rails with daemon option

Add Action Cable notifications to instrument guide [ci skip]

Related to #29417

Related to #29176

Add process.action_mailer notification to Instrument guide [ci skip]

Added test case for starting rails with daemon option, this should set the option[:daemonize] to true, otherwise the option[:daemonize] will be set to false

This has been added by 8f8cb1ba.
But now it is unnecessary because it is not used in the test.

Bump RuboCop 0.50.0

Yield with an error instance instead of error class

RuboCop 0.50.0 was released.
https://github.com/bbatsov/rubocop/releases/tag/v0.50.0

And `rubocop-0-50` channel is available in Code Climate.
https://github.com/codeclimate/codeclimate-rubocop/issues/107#issuecomment-336234260

This commit will bump RuboCop to 0.50.0.
There are no new offences in this change.

```console
% bundle exec rubocop --version
0.50.0
% bundle exec rubocop
Inspecting 2350 files

(snip)

2350 files inspected, no offenses detected
```

fix the description for the `select_all` [ci skip]

[ci skip]Enable link to ActionDispatch::Integration::Session#process in rdoc

Fix "warning: assigned but unused variable - message"

Ruby 2.5 warns about this. Ref: https://travis-ci.org/rails/rails/jobs/286338999

Fix some typos [ci skip]

Add allow_other_host option to redirect_back method

Update security guide for signed cookie rotations

The example was slightly incorrect. This commit also adds a test case
for this example to cookies middleware unit tests.

Improve railties' tests

Include Mutex_m into GeneratedAttributeMethods instead of extending instance

Simplify parse arguments in `ConsoleTest`

Express #change_column_comment as public api

Use released `sidekiq` instead of master version