CE: Override module to specify that we're overriding

What does this MR do?

CE port of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3876

Why was this MR needed?

We're not really using this in CE, but it doesn't hurt to have it and reduce the difference between CE and EE. Also the doc is in CE, too.

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend

What are the relevant issue numbers?

See https://gitlab.com/gitlab-org/gitlab-ee/issues/1819