[DISCUSS] [RIP-39] Support gRPC protocol

[Zhouxiang Zhan]

Hi. RocketMQ Community:

We are proposing to implement the gRPC protocol on RocketMQ.

Detailed proposal: https://shimo.im/docs/gXqmeEPYgdUw5bqo/ 「RIP-39：Support
gRPC protocol」

Looking forward to more detailed discussions.