Follow-up propagate integrations service

What does this MR do?

This is a follow-up from !32331 (merged).

• Use Gitlab::Utils.to_boolean instead of ActiveRecord::Type::Boolean.new.cast(params[:overwrite]) !32331 (diffs, comment 346148538)
• Replace SQL statement with ActiveRecord !32331 (diffs, comment 346142238)
  • I see here an opportunity to move the query to the model but I've decided to keep the duplication because PropagateServiceTemplate will be removed at some point in the future and Project class is already very long (2593 lines at the moment).

Related to #199388 (closed)