Upload LFS objects to Object Storage via Workhorse

What

Use workhorse to perform object storage uploads asking unicorn only to authorize and finalize the upload. Use the LFS protocol to return a signed upload URL to the client which LFS will used to upload direct to S3 compatible storage.

Why

We still want to have full control over the upload process, so we can at least save unicorn resources and upload to object storage while workhorse receives the object.

How

1. Introduce ObjectStorage uploader in workhorse: gitlab-workhorse!227 (merged)
2. Unify upload handling in workhoorse: gitlab-workhorse!230 (merged)
3. Drive workhorse feature activation via API call gitlab-org/gitlab-ee!4794

Related

• https://gitlab.com/gitlab-org/gitlab-ee/issues/2841
• https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2760
• LFS documentation: https://github.com/git-lfs/git-lfs/blob/master/docs/api/basic-transfers.md#uploads and https://github.com/git-lfs/git-lfs/blob/master/docs/api/batch.md