When file_mover_spec.rb ran, it would initialize fog-aws with
`Fog::AWS::Storage::Real` service instead of `Fog::AWS::Storage::Mock`
because `Fog.mock!` was not called. Ensure that we use
`stub_uploads_object_storage` to prevent that from happening.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/64083

It persist temporary personal snippets under
user/:id namespaces temporarily while creating
a upload record to track it. If an user gets removed
while it's still a tmp upload, it also gets removed.
If the tmp upload is sent, the upload gets moved to
personal_snippets/:id as before. The upload record
also gets updated to the new model type as well.

Previously one could move any temp/ sub folder around.

Currently we pass temp file path to FileMover

This reverts commit 54a575f1, reversing
changes made to c63af942.

Move uploads to object storage

Closes #4163

See merge request gitlab-org/gitlab-ee!3867

Use uploads/system directory for personal snippets

See merge request !2123