Rename identifier_for_subject method to identifier_for_repositorable
What does this MR do?
In #39176 (closed) we're allowing resources other than projects to have repositories attached. Therefore, we need to refactor those places where we use project because it can also be a snippet. Besides, we need to abstract this variable to something like repositorable.
In this MR we rename the method GlRepository::RepoType#identifier_for_subject to identifier_for_repositorable to align with this.