Update README.rdoc [ci skip]

Highlighted code
Update commands.rb content in initialization guide

[ci skip]
Add section for command_tasks in initialization guide

[ci skip]
Change syntax format for example returned values

According to our guideline, we leave 1 space between `#` and `=>`, so we
want `# =>` instead of `#=>`.

Thanks to @fxn for the suggestion.

[ci skip]
Fix RailsServer#start content in initialization guide

[ci skip]
[ci skip] Replace #=> with # =>
Correct guide relating MiddlewareStackProxy with Enumerable

[ci skip] Enumerable.instance_methods &
Rails::Configuration::MiddlewareStackProxy.instance_methods # =>
[:as_json]

MiddlewareStackProxy does not share any notable methods with Enumerable.
Remove outdated guide on using rack builder w/o rails middleware

[ci skip]
Fix broken Wikipedia link.
Update action_controller_overview.md [ci skip]

Code style adherence
The option is called encode_big_decimal_as_string [ci-skip]
Fix bad test order dependency between test/cases/validations/i18n_generate_message_validation_test.rb and test/cases/validations/uniqueness_validation_test.rb
Fix bad test order dependency between LoadAllFixturesTest#test_all_there and FoxyFixturesTest#test_ignores_belongs_to_symbols_if_association_and_foreign_key_are_named_the_same
[ci skip] typo in ArgumentError exception
Merge pull request #12916 from petervandenabeele/typo_4_0_release_notes

[ci skip] typo in ArgumentError in 4_0_release_notes.md
Merge pull request #12911 from zenspider/test_order_dependency_fixes

Test order dependency fixes
avoiding iterations and calling of underscore on all elements of array
Merge pull request #12917 from akshay-vishnoi/refactor

avoiding iterations and calling of underscore on all elements of array
Instrument each load config initializer

In order to simplify profiling loading of initializers,
added instument for tracking load config initializer event from
`config/initializers`
Merge pull request #12859 from jetthoughts/track_initializers_loading

Track initializer's loaded event per file