Move checksum test for ReplicateRepository to ReplicateRepository itself
For replication of a repository, Gitaly tries to standardize on ReplicateRepository. As such the RPC should be as solid as it can be.
One thing that's now left to the caller, is the execution of checksums. This makes it error prone. To fix this issue, add a SkipChecksum
field to the proto, and with that default to checksumming unless the caller has a good reason not to, like with Praefect.
/cc @nnelson @proglottis