Enable remaining settings

- use_cookies_with_metadata
  Provided extra options for cookies. Existing cookies will work fine.
  https://github.com/rails/rails/issues/36546
- return_only_media_type_on_content_type
  Include the charset in the content type. Looking at the headers that
  are being returned, it already did this.
- Use Zeitwerk as the autoloader
  https://github.com/fxn/zeitwerk

config/initializers/new_framework_defaults_6_0.rb

@@ -14,10 +14,10 @@ Rails.application.config.action_view.default_enforce_utf8 = false
 #
 # This option is not backwards compatible with earlier Rails versions.
 # It's best enabled when your entire app is migrated and stable on 6.0.
-# Rails.application.config.action_dispatch.use_cookies_with_metadata = true
+Rails.application.config.action_dispatch.use_cookies_with_metadata = true
 
 # Change the return value of `ActionDispatch::Response#content_type` to Content-Type header without modification.
-# Rails.application.config.action_dispatch.return_only_media_type_on_content_type = false
+Rails.application.config.action_dispatch.return_only_media_type_on_content_type = false
 
 # Return false instead of self when enqueuing is aborted from a callback.
 Rails.application.config.active_job.return_false_on_aborted_enqueue = true
@@ -49,5 +49,4 @@ Rails.application.config.active_record.collection_cache_versioning = true
 # classes should be defined. It also requires that constants are not autoloaded in initializers.
 # Enabling Zeitwerk would be good, but it'll take some work. Using the :classic autoloader gives
 # us the same autoloading that Rails 5.2 had.
-# Rails.application.config.autoloader = :zeitwerk
-Rails.application.config.autoloader = :classic
+Rails.application.config.autoloader = :zeitwerk