Support Direct Upload for Uploads to Object Storage

Much of the groundwork for Direct Object storage has been done, including

• Object Storage Direct Object Uploader: https://gitlab.com/gitlab-org/gitlab-ee/issues/4184
• Move uploads to object storage: https://gitlab.com/gitlab-org/gitlab-ee/issues/4163 and https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3867
• Direct upload with LFS: gitlab-workhorse!227 (merged)
• Direct upload to Object Storage for artifacts: gitlab-workhorse!238 (merged)

My understanding was that the remaining work to support object uploads was in workhorse, but, from a discussion today with @ayufan, it became apparent that there is work left to be done on supporting Direct Object Storage Uploads for "Uploads" (this is a confusing sentence, I know).

I am not sure of the technical details of this implementation, but, while this is very late to bring to the table, we should try and get it scheduled in %10.7 if possible.

cc @smcgivern @victorwu @nolith @ayufan @joshlambert