Add information about 'available_locales' and 'enforce_available_locales'
to the configuring guide.

Closes #13202. [ci skip]

The flag will be used in multiple places to check for errors during runtime if enabled.

Source:  https://github.com/rails/sprockets-rails/pull/100

[ci skip]

[ci skip]

[ci skip]

added schema_migrations_table_name to ActiveRecord::Base in order that the name of the schema migrations table can be configured.

consolidated test_schema_migrations_table_name tests

Added changelog entry

edited changelog

removed commented lines

removed reader

ensure the schema migrations table is reset at end of test

added entry to configuration guide

guides typo and changelog order

:after_initialize runs after config/initializers, not before

See `actionpack/test/controller/parameters/raise_on_unpermitted_params_test.rb`

This option was removed from master.

[ci skip]

[ci skip]

Update configuration docs for assets.enabled, as it's set true by default in the configuration and doesn't appear in the config files anymore.

Same rationale as previous revert.

This reverts commit 887225e6.

It is not in the contract that flags have to be singletons,
the use of regular font indicates that.

This reverts commit 80036f9a.

/cc @fxn

We discussed that the auto explain feature is rarely used.
This PR removes only the automatic explain. You can still display
the explain output for any given relation using `ActiveRecord::Relation#explain`.

As a side-effect this should also fix the connection problem during
asset compilation (#9385). The auto explain initializer in the `ActiveRecord::Railtie`
forced a connection.

Capitalization in the title of the section, enumerates the environments
in the usual order, adds a paragraph, and tries to use less "you"s.

Replaced documentation for config.action_controller.raise_on_unpermitted_parameters with documentation for config.action_controller.action_on_unpermitted_params.