IAP support for SSH connection

### Dependencies

### Feature Request
My company uses IAP to access GCP vm's almost exclusively. I cannot use the cloud plugin because it tries to use a public or private IP for the SSH connections.

Could be possible to allow the use of IAP for ssh connections? If full inegration is difficult, just allowing some sort of custom ssh connection setup would be enough. (Being able to setup an ssh proxy with gcloud before trying to connect for example)