Derived from the discussion here.
#28480 implements a client that only decodes the metadata part of an object. It's useful for garbage collector, or any other components that only care about the object's metadata. However, #28480 only works with JSON, not with Protobuf.

To support both content types, and to make the client simpler, it's desirable to let api server support list/get/watch of the ObjectMeta for a resource, and convert it to a specific version of ObjectMeta that the client requests for.

@smarterclayton @lavalamp