Optimize distributed deletions from gRPC

[MichaelScofield]

What type of enhancement is this?

Refactor

What does the enhancement do?

GRPC delete requests are just like insert requests, carrying the column data for deletions. They both had very similar implementations: splitting the to be inserted/deleted data by partition rules, not parallel or batched, and done in a per table fashion etc.

Now the distributed insertions are optimized in a batch in #1687 , it's time we do that for distributed deletions as well.

Implementation challenges

No response

[NiwakaDev]

I'd like to work on this issue. Should I first start by implementing DeleteRequests like InsertRequests?:
GreptimeTeam/greptime-proto#47

[MichaelScofield]

@NiwakaDev Yes, I think we should first implement it.