API for configuring repository pull mirroring via SSH
Follow up to https://gitlab.com/gitlab-org/gitlab-ee/issues/1499
We support HTTP and SSH pull mirroring via the UI but the API only supports HTTP. We should aim for consistency.
Adding SSH support is more difficult because of the backwards and forwards interaction required to configure it.
Proposal
TBD
Links / references
https://docs.gitlab.com/ee/workflow/repository_mirroring.html#pulling-from-a-remote-repository