Log cause of the failed reference update

When Prepare() or Commit() method of the Updater was called inside UpdaterWithHooks#UpdateReference method the errors returned were thrown away. Because of it we were missing important part of the failure cause - the output of the failed git operation. In order to fix it now we return it as part of the Error instance. Because returned error is a structured error with metadata assigned to it this metadata will be logged by the interceptors around gRPC method. The metadata is not returned to the RPC caller, so there are no changes to the existing API.

Closes: #4677 (closed) Changelog: added