Praefect: storage scoped RPCs not handled properly

Scope of the FindRemoteRepository RPC call changed to STORAGE as it should be redirected to one of the existing in the system gitaly nodes. The storage parameter was added previously and now passed from the clients to the Praefect with each call (gitlab!35962 (merged)).

Coordinator changed to properly handle STORAGE and SERVER scoped requests.
Each STORAGE scoped mutator operations will be propagated to all gitaly nodes, while accessor operations is served by the primary node. As accessor operations could be distributed over secondaries the #2972 (closed) was created to track it.
SERVER scoped requests handled as before: all requests go to the primary of the first virtual storage configured.

Closes: #2442 (closed)