[10.4.4 port] Resolve "PrepareUntrackedUploads PostgreSQL syntax error"

What does this MR do?

Ports https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17019 to 10.4.4.

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

I left out the last commit of that MR which is just a spec refactor.

Why was this MR needed?

Merge conflicts with 10.4.4: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17019#note_59096389

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• 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-qa manual pipeline job)

What are the relevant issue numbers?