Add independent TSO service

[binshi-bing]

Feature Request

To separate TSO into an independent service #5836, we define a new TSO service in protobuf to wraps up all the TSO related rpcs, then we can start a gPRC server which provides TSO service only.

Describe the feature you'd like

Tasks

• Define a new TSO service in protobuf
• Implement TSO gPRC server
• Implement TSO gPRC client

Describe alternatives you've considered

Without defining a new TSO service in protobuf, the TSO microservice needs to be provided by the original all-in-one PD gPRC server which also registers all other services and initializes all configurations and many other things unnecessarily. It will be harder to decouple TSO service/module from other services/modules and to evolve to an independent Tenant TSO service.

Teachability, Documentation, Adoption, Migration Strategy

[binshi-bing]

I'll re-create this issue with type "development task" instead of "feature request"

[binshi-bing]

It seems that I can't close it and mark it as abandoned.