Server side implementation of paging for etcd3

Add a feature gate in the apiserver to control whether paging can be
used. Add controls to the storage factory that allow it to be disabled
per resource. Use a JSON encoded continuation token that can be
versioned. Create a 410 error if the continuation token is expired.

Adds GetContinue() to ListMeta.

pkg/controller/garbagecollector/garbagecollector_test.go

@@ -420,6 +420,7 @@ func TestGCListWatcher(t *testing.T) {
 		t.Fatal(err)
 	}
 	lw := listWatcher(client, podResource)
+	lw.DisablePaging = true
 	if _, err := lw.Watch(metav1.ListOptions{ResourceVersion: "1"}); err != nil {
 		t.Fatal(err)
 	}