Add an ssh/scp cache type for runners
Problem to solve
Runners cache only allow s3/gcs types, it's quite useful for runners running on AWS or GCP, but we have some runners on MacStadium to use Xcode and it could be expensive to pay for the data transfer of these storages.
Proposal
I'd like to have the chance to get/put cache remotely to any Linux/Unix machine thru SSH (using SCP or similar tools), so we just need to have a server listening for SSH on the private network and have a user/password or ssh-key that allows access from the runner to put/get files on a certain remote folder.
What does success look like, and how can we measure that?
We could have cache stored remotely without using NFS or another kind of hacks to share folders between runners.