Resolve "Move EE-only frontend files into ee/ subdirectory"

What does this MR do?

This moves EE-specific JS files to ee/app/assets/javascripts.

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

Why was this MR needed?

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Frontend
• 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 #4536 (closed)