Proposal to add service metadata report feature

[nobodyiam]

Service metadata information is very important to service governance, e.g. app name, service name, method parameters' name and type information.
Without these information, it's very hard to implement features like service test, service mock, service router rule, etc.
So I think we need to design a mechanism in sofa rpc to report the service metadata, which then could be integrated with different service metadata center implementations, e.g. opensergo.

Dubbo has refactored and supported reporting service metadata since 2.7.0.

[seeflood]

Looks good. With these metadata, projects like MOSN and Layotto can do protocol conversion

[MingJunDuan]

Good, with these metadata, sofa-rpc can provide online-invoke function from admin page