Move EE specific code out of lib/gitlab

What does this MR do?

This is the CE backport of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9831, containing changes that have to be made to CE to keep the two codebases the same.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/9505

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Security reports checked/validated by reviewer