WIP: Add test for backup/restore task

Adds a QA test on gitlab-ce to test both backup and restore using https://gitlab.com/gitlab-org/gitlab-qa/

Closes gitlab-qa#22 (moved)

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)