Add gRPC admin health check
This is groundwork for the gRPC admin deploy API. We add two new optional gRPC listeners: admin-unix and admin-https. In the future it will be mandatory to configure at least one. The listeners use per-request bearer token authentication. Token authentication is mandatory.
The only RPC added in this change is a health check. Once that is working in gitlab-ce and omnibus we can start adding more useful RPC's.
Edited by Jacob Vosmaer