API for configuring repository push mirroring via SSH
### Problem to solve We support HTTP and SSH push mirroring via the UI but not the API only. ### Further details Adding SSH support is more difficult because of the backwards and forwards interaction required to configure it. ### Proposal Implement API support for SSH push mirroring ### Links / references https://docs.gitlab.com/ee/user/project/repository/repository_mirroring.html#pushing-to-a-remote-repository-core
issue