Resolve "Move EE-only /lib files under top-level /ee directory"

What does this MR do?

Moves EE-specific lib/ files to ee/lib/.

Are there points in the code the reviewer needs to double check?

I don't think so.

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #3971 (closed)