Inline JSON: GameServerAllocation v1.LabelSelector

The K8s YAML library will inline embeded structs, but some other ones
will not. So adding the `json:",inline"` hint, so that they know that
the `v1.LabelSelector` should be inlined if people are so inclined to
reference it via Golang yaml libraries.

Closes googleforgames#2853

pkg/apis/allocation/v1/gameserverallocation.go

@@ -100,7 +100,7 @@ type GameServerAllocationSpec struct {
 // a GameServer for allocation.
 type GameServerSelector struct {
 	// See: https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/
-	metav1.LabelSelector
+	metav1.LabelSelector `json:",inline"`
 	// [Stage:Beta]
 	// [FeatureFlag:StateAllocationFilter]
 	// +optional