Resolve "GitLab Project export should use object storage"

What does this MR do?

This is for the export only

• Adds a feature flag to enable/disable Object Storage
• Uses an uploader when this flag is true
• Uses the old code when the flag is false
• When an export already has a file using the old cose, uses that regardless of the flag

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

Haven't tested if it actually works on object storage the way we have in GitLab

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #46246 (closed)