Update admin notifications translatable fields

The same way we did for banners.

We needed to add new translation keys so the labels are displayed in the
correct language. I've kept the original `title` and `body` attributes
so they can be used in other places.

While backporting, we also added the original translations because they
hadn't been backported yet.

app/controllers/admin/admin_notifications_controller.rb

@@ -63,8 +63,7 @@ class Admin::AdminNotificationsController < Admin::BaseController
   private
 
     def admin_notification_params
-      attributes = [:title, :body, :link, :segment_recipient,
-                    *translation_params(AdminNotification)]
+      attributes = [:link, :segment_recipient, translation_params(AdminNotification)]
 
       params.require(:admin_notification).permit(attributes)
     end