Draft: praefect/service: RepositoryReplicas RPC fails if a replica does not exist
requested to merge bill2022/gitaly:4051-repository-replicas-rpc-can-output-a-replica-unavilable into master
Because the original error message is not dictating ''a replica does
not yet exist on the host" when the repository is not replicated yet
to all the hosts. So in this commit, check whether the error gets from
the CalculateChecksum Grpc call is dataloss or not. If it is dataloss,
then return a more suitable error message.
Related to #4051