Move EE-specific JavaScript files to ee/app/assets/javascripts

CE port of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/4633.

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?