Resolve "Move EE-specific `changelogs/unreleased-ee/` files to `ee/changelogs/unreleased/`"

What does this MR do?

This moves EE-specific changelog items to ee/changelogs/unreleased.

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

I don't think so, release-tools is ready: release-tools!292 (merged), and bin/changelog is too.

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

What are the relevant issue numbers?

Closes #4947 (closed)