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_setting_extension.rb

@@ -95,6 +95,10 @@ module SiteSettingExtension
     @shadowed_settings ||= []
   end
 
+  def requires_confirmation_settings
+    @requires_confirmation_settings ||= {}
+  end
+
   def hidden_settings_provider
     @hidden_settings_provider ||= SiteSettings::HiddenProvider.new
   end
@@ -244,6 +248,7 @@ module SiteSettingExtension
           secret: secret_settings.include?(s),
           placeholder: placeholder(s),
           mandatory_values: mandatory_values[s],
+          requires_confirmation: requires_confirmation_settings[s],
         }.merge!(type_hash)
 
         opts[:plugin] = plugins[s] if plugins[s]
@@ -654,6 +659,14 @@ module SiteSettingExtension
 
       mandatory_values[name] = opts[:mandatory_values] if opts[:mandatory_values]
 
+      requires_confirmation_settings[name] = (
+        if SiteSettings::TypeSupervisor::REQUIRES_CONFIRMATION_TYPES.values.include?(
+             opts[:requires_confirmation],
+           )
+          opts[:requires_confirmation]
+        end
+      )
+
       categories[name] = opts[:category] || :uncategorized
 
       hidden_settings_provider.add_hidden(name) if opts[:hidden]