Configure Rails/I18nLocaleAssignment cop to scan all Ruby files

This cop scans only the tests files by default, but we prefer to scan all
application Ruby files, so when a developer uses the class method
`I18n.locale=`, the cop will embrace using the method
`I18n.with_locale` instead. By doing this way, the cop will help
developers to avoid unexpected translation errors.

Quoting the Rails 6 guides:
> I18n.locale can leak into subsequent requests served by the same
thread/process if it is not consistently set in every controller. For
example executing I18n.locale = :es in one POST requests will have
effects for all later requests to controllers that don't set the locale,
but only in that particular thread/process. For that reason, instead of
I18n.locale = you can use I18n.with_locale which does not have this
leak issue.

Now we enabled the cop for all application Ruby files; we have to
remove the assignments at the controller level to set the request
locale. As Rails 6 guides suggest [1], we can use the `around_action`
controller callback to set each request locale without breaking the
rule.

This cop will warn CONSUL developers when using `I18n.locale`
assignment embracing them to use the `I18n.with_locale`instead.

[1] https://guides.rubyonrails.org/i18n.html#managing-the-locale-across-requests

.rubocop.yml

@@ -269,6 +269,8 @@ Rails/HttpStatus:
 
 Rails/I18nLocaleAssignment:
   Enabled: true
+  Include:
+    - "**/*.rb"
 
 Rails/InverseOf:
   Enabled: true