Adding new label to indicate what is managing an EndpointSlice

This adds a new Label to EndpointSlices that will ensure that multiple
controllers or entities can manage subsets of EndpointSlices. This
label provides a way to indicate the controller or entity responsible
for managing an EndpointSlice.

To provide a seamless upgrade from the alpha release of EndpointSlices
that did not support this label, a temporary annotation has been added
on Services to indicate that this label has been initially set on
EndpointSlices. That annotation will be set automatically by the
EndpointSlice controller with this commit once appropriate Labels have
been added on the corresponding EndpointSlices.

pkg/controller/endpointslice/utils_test.go

@@ -58,7 +58,10 @@ func TestNewEndpointSlice(t *testing.T) {
 
 	expectedSlice := discovery.EndpointSlice{
 		ObjectMeta: metav1.ObjectMeta{
-			Labels:          map[string]string{discovery.LabelServiceName: service.Name},
+			Labels: map[string]string{
+				discovery.LabelServiceName: service.Name,
+				discovery.LabelManagedBy:   controllerName,
+			},
 			GenerateName:    fmt.Sprintf("%s-", service.Name),
 			OwnerReferences: []metav1.OwnerReference{*ownerRef},
 			Namespace:       service.Namespace,