DEV: Add endpoint for dismissing outdated translations (#22509)

Recently we started giving admins a notice in the advice panel when their translations have become outdated due to changes in core. However, we didn't include any additional information.

This PR adds more information about the outdated translation inside the site text edit page, together with an option to dismiss the warning.

app/serializers/site_text_serializer.rb

@@ -1,7 +1,15 @@
 # frozen_string_literal: true
 
 class SiteTextSerializer < ApplicationSerializer
-  attributes :id, :value, :interpolation_keys, :has_interpolation_keys?, :overridden?, :can_revert?
+  attributes :id,
+             :value,
+             :status,
+             :old_default,
+             :new_default,
+             :interpolation_keys,
+             :has_interpolation_keys?,
+             :overridden?,
+             :can_revert?
 
   def id
     object[:id]
@@ -11,6 +19,22 @@ class SiteTextSerializer < ApplicationSerializer
     object[:value]
   end
 
+  def status
+    if override.present?
+      override.status
+    else
+      "up_to_date"
+    end
+  end
+
+  def old_default
+    override.original_translation if override.present?
+  end
+
+  def new_default
+    override.current_default if override.present?
+  end
+
   def interpolation_keys
     object[:interpolation_keys]
   end
@@ -23,9 +47,15 @@ class SiteTextSerializer < ApplicationSerializer
     if options[:overridden_keys]
       options[:overridden_keys].include?(object[:id])
     else
-      TranslationOverride.exists?(locale: object[:locale], translation_key: object[:id])
+      override.present?
     end
   end
 
   alias_method :can_revert?, :overridden?
+
+  private
+
+  def override
+    TranslationOverride.find_by(locale: object[:locale], translation_key: object[:id])
+  end
 end