FEATURE: Introduce site settings which require confirmation (#27315)

Many site settings can be distructive or have huge side-effects
for a site that the admin may not be aware of when changing it.

This commit introduces a `requires_confirmation` attribute that
can be added to any site setting. When it is true, a confirmation
dialog will open if that setting is changed in the admin UI,
optionally with a custom message that is defined in client.en.yml.

If the admin does not confirm, we reset the setting to its previous
clean value and do not save the new value.

lib/site_settings/type_supervisor.rb

@@ -20,12 +20,15 @@ class SiteSettings::TypeSupervisor
     list_type
     textarea
     json_schema
+    requires_confirmation
   ].freeze
   VALIDATOR_OPTS = %i[min max regex hidden regex_error json_schema].freeze
 
   # For plugins, so they can tell if a feature is supported
   SUPPORTED_TYPES = %i[email username list enum].freeze
 
+  REQUIRES_CONFIRMATION_TYPES = { simple: "simple", user_option: "user_option" }.freeze
+
   def self.types
     @types ||=
       Enum.new(