Direct upload of artifacts

What does this MR do?

This implements direct upload of artifacts, which can be supported on Google Cloud only for now, due to Content-Length.

This is not yet nicest code, but should work.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• 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)

What are the relevant issue numbers?