Add timezone to current_user_serializer (#8448)

* the code to get current user already got their
  user_option record as well, so adding the timezone
  column to the attributes returned should not create
  any additional overhead. this timezone will be very
  useful for getting momentjs dates relative to the
  user's timezone

app/serializers/current_user_serializer.rb

@@ -44,7 +44,8 @@ class CurrentUserSerializer < BasicUserSerializer
              :groups,
              :second_factor_enabled,
              :ignored_users,
-             :title_count_mode
+             :title_count_mode,
+             :timezone
 
   def groups
     object.visible_groups.pluck(:id, :name).map { |id, name| { id: id, name: name.downcase } }
@@ -106,6 +107,10 @@ class CurrentUserSerializer < BasicUserSerializer
     object.user_option.redirected_to_top
   end
 
+  def timezone
+    object.user_option.timezone
+  end
+
   def can_send_private_email_messages
     scope.can_send_private_messages_to_email?
   end