rambohe

@Sodawyx beside `/version` request, we need to handle `apps/discovery.k8s.io/v1` and `apps/discovery.k8s.io/v1beta1` resource requests.

@Sodawyx I think it's not a good idea to modify `local proxy` and `cache manager`, maybe we can handle the above requests by adding new handlers only. take `/version` for...

> @rambohe-ch Sounds good, it can simplify the logic in CacheManager. Since proxyServer and yurthub server listen at different port, it may need another redirection in local proxy. > >...

> @Congrool yes, we need to add `/version` handler in yurthub proxy server for getting version info of kube-apiserver. and i have updated the above example as following: 

@Sodawyx small modifications for comments: ``` apps/discovery.k8s.io/v1 --> apis/discovery.k8s.io/v1 apps/discovery.k8s.io/v1beta1 --> apis/discovery.k8s.io/v1beta1 ```

> I think the disscussion above means to add a new http handler for proxy server to handle `/version` request. Something like: > > ```go > mux := http.NewServeMux() >...

@Sodawyx please add unit tests for newly added code.

@Sodawyx please fix errors from github ci pipeline.

/lgtm /approve

/backport release-v0.7