Adds Identity#for_user for use in an EE MR
What does this MR do?
Adds a scope to avoid a rubocop warning in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5817#note_169598189
Adds a scope to avoid a rubocop warning in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5817#note_169598189