Allow to store uploads by default on Object Storage

What does this MR do?

Introduce direct_upload option for uploads which is gonna set a default storage to Object Storage.

When used it uses Unicorn to save data, so it is suitable only for small uploads on fast egress networks.

This is first iteration before we move to direct accelerated uploads with Workhorse.

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?

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/44663