Subtask from #17191

A go program that will fetch discovery info from all federated servers and provide a summarized view.

In addition to the discovery information that apiservers currently surface, we need to add a server URL.

Open questions:

• Extend the existing APIGroupList (

  kubernetes/pkg/api/unversioned/types.go

  Line 307 in e108a32

  type APIGroupList struct {

  ) and add a server URL there or define a new one?
• Return the appropriate server URL for internal and external clients.
  • Do we want to do this?
  • Can we auto detect if the request is from a client inside the cluster or external?
  • Or should the request have a way to specify that?
  • How does the client figure out that is it inside the cluster for master or not?

@kubernetes/sig-api-machinery @kubernetes/goog-csi @smarterclayton @lavalamp @thockin @bgrant0607