Refactor GRPC clients management

[MichaelScofield]

What type of enhancement is this?

Tech debt reduction

What does the enhancement do?

Currently the GRPC clients management is a little chaos, there is ChannelManager for caching raw tonic channels, and there is DatanodeClients for managing Datanode GRPC clients for Frontend. This makes our codes hard to understand, and may introduce bugs hard to trace like memory leaks.

I think a redesign of our GRPC clients management is necessary, to alleviate the pain of debugging efforts.

Implementation challenges

No response

[MichaelScofield]

too broad