[Feature] Support to override velaux-apiserver

[nuclearwu]

Is your feature request related to a problem? Please describe.

Most adopters introduce kubevela without modifying the kubevela(vela-core and vela cli), instead modify velaux to suit our own scenarios. Therefore, we keep some of the interfaces in apiserver, modify some of the interfaces or models, and then add some more. Although #740 adds a backend plugin framework to support developing extended apiserver, but velaux-apiserver itself does not have standardized rewriting or secondary development capabilities.

So, we want velaux-apiserver to open up some rewritten methods or add frameworks to enable adopters to introduce kubevela and velaux as dependencies to build an aggregate apiserver by rewriting and adding parts of the interface or model.

Describe the solution you'd like

open up velaux-apiserver some rewritten methods or frameworks to enable adopters to introduce kubevela and velaux as dependencies to build an aggregate apiserver by rewriting and adding parts of the interface or model.

Refactorpkg/server/config/config.go, pkg/server/server.go, pkg/server/domain/service/service.go, pkg/server/interfaces/api/interfaces.go according to the extensible and rewritable principles.

1. Override config.go to support add ExtensionServerConfig.
2. Override the Run method of server.go to support register ExtensionAPIRoute.
3. Override service.go to support init ExtensionServiceBean.
4. Override interfaces.go to support init ExtensionAPIBean.

[nuclearwu]

@wonderflow @barnettZQG @chivalryq