All this has been simplified.

fix typo in CHANGELOGs.

[Matilda Smeds & Xavier Noria]

- Also deprecate passing {required} to the model generator.
- Also made sure the global config `belongs_to_required_by_default` is
  applied correctly to the model generator for `null: false` option.

See rationale in the warning message included in the patch.

We introduced `connection` option for specifying spec with 1acd9a64.
But now we are using the `database` to specify the same value in other commands.

* https://github.com/rails/rails/blob/0a0f115031b64b5335fa88543c40df4194dfb428/activerecord/lib/rails/generators/active_record/migration/migration_generator.rb#L11
* https://github.com/rails/rails/blob/0a0f115031b64b5335fa88543c40df4194dfb428/activerecord/lib/rails/generators/active_record/model/model_generator.rb#L17

The options provided to the users should be uniform. Since the term
"database" is used in rake task etc, So I want to be able to use it in
`dbconsole` command.

Also I deprecated the `connection` option because I think that it
would be confusing if there are multiple options to specify a same value.

* add leading `#` before `=>` since hash rocket is valid Ruby code
* add backticks
* remove trailing spaces
* and more

A long-running `rails console --sandbox` could cause a database server
to become out-of-memory as it's holding on to changes that happen on the
database.

Given that it's common for Ruby on Rails application with huge
traffic to have separate write database and read database, we should
allow the developers to disable this sandbox option to prevent someone
from accidentally causing the Denial-of-Service on their server.

[Alex Kitchens, Prathamesh Sonpatki]

This allows specifying the environment as would any other rails commands.

* Update RAILS_VERSION
* Bundle
* rake update_versions
* rake changelog:header

- If you have hashes inside array, the hashes were getting initialized
  as regular HWIA wereas we want them to be
  NonSymbolAccessDeprecatedHash in order to trigger a deprecation
  warning when keys are accessed with string.

  This patch fixes that by overwriting the `[]=` to to the same
  as what HWIA does (with the difference that we don't call
  `convert_key` to not trigger a deprecation when setting value).

  I also took the liberty to extract `hash.nested_under_indifferent_access`,
  into a separate method to allow subclasses to return whatever
  they want.
  Inheriting HWIA is not common, but I think it's useful for cases
  like this one where we want to preprocess reading and writing values
  in the hash (for deprecation purposes or other reasons).

A change to `Rails::Application.config_for` in
https://github.com/rails/rails/pull/33815 and
https://github.com/rails/rails/pull/33882 has altered the behaviour of
the returned object in a breaking manner. Before that change, nested
hashes returned from `config_for` could be accessed using non-symbol keys.
After the change, all keys are recursively symbolized so non-symbol access
fails to read the expected values.

This is a breaking change for any app that might be relying on the
nested hashes returned from `config_for` calls, and thus should be
deprecated before being removed from the codebase.

This commit introduces a temporary `NonSymbolAccessDeprecatedHash` class
that recursively wraps any nested hashes inside the `OrderedOptions`
object returned from `config_for` and issues a deprecation notice when a
non-symbol based access is performed.

This way, apps that are still relying on the ability to access these
nested hashes using non-symbol keys will be able to observe the
deprecation notices and have time to implement changes before non-symbol
access is removed for good.

A CHANGELOG entry is also added to note that non-symbol access to nested
`config_for` hashes is deprecated.

During the development of #33145, I have named a few concepts in the
code as `whitelisted`. We decided to stay away from the term and I
adjusted most of the code afterwards, but here are the cases I forgot to
change.

I also found a case in the API guide that we could have cleaned up as
well.

[ci skip]

This reverts commit fa791fb8.

Reason: `server` argument was deprecated in Rails 6.0. Ref: #32058.