Track Additional Comments for the RPC Interactions of VolumeSnapshot and GroupVolumeSnapshot #554

Is your feature request related to a problem?/Why is this needed

If the implementation of the SP's group snapshot function is flawed, for example, if two data volumes are snapshotted at the same time, one will succeed and the other will always fail, then no matter how many times CO retries the call, it will not get the expected results. It maybe lead to a deadlock in CO. But in the spec, I can't find a suitable status code to tell CO not to retry.

Describe the solution you'd like in detail

As @bswartz said,

The only other solution I can see is to return a "successful" snapshot but mark it as broken or partial with some explicit boolean
value in the response message. This would allow the CO to stop retying and then decide whether to keep the broken group snapshot or clean it up the normal way.

Additional context

See #545 (comment) and #545 (comment)