Project exports should not rely on a shared nfs file server and instead use object storage

The directory

/var/opt/gitlab/gitlab-rails/shared/tmp/project_exports 

is an NFS mount that is shared between the front-end and sidekiq fleet on GitLab.com. This directory is used for temporary storage for when project exports are downloaded. It would benefit HA deployments if this is moved to object storage so that having a shared filesystem is no longer necessary.

This is important to gitlab.com because this nfs mount is a single point of failure for gitlab.com and ties into our availability goals.