📖 update webhooks for core types to match cr 0.15

Signed-off-by: Mikko Ylinen <mikko.ylinen@intel.com>

docs/book/src/reference/webhook-for-core-types.md

@@ -9,43 +9,29 @@ in controller-runtime.
 It is suggested to use kubebuilder to initialize a project, and then you can
 follow the steps below to add admission webhooks for core types.
 
-## Implement Your Handler
+## Implement Your Webhook
 
-You need to have your handler implements the
-[admission.Handler](https://pkg.go.dev/sigs.k8s.io/controller-runtime/pkg/webhook/admission?tab=doc#Handler)
+You need to have your webhook to implement the
+[admission.Defaulter](https://pkg.go.dev/sigs.k8s.io/controller-runtime/pkg/webhook/admission?tab=doc#Defaulter)
 interface.
 
 ```go
-type podAnnotator struct {
-	Client  client.Client
-	decoder *admission.Decoder
-}
+type podAnnotator struct {}
 
-func (a *podAnnotator) Handle(ctx context.Context, req admission.Request) admission.Response {
-	pod := &corev1.Pod{}
-	err := a.decoder.Decode(req, pod)
-	if err != nil {
-		return admission.Errored(http.StatusBadRequest, err)
-	}
+func (a *podAnnotator) Default(ctx context.Context, obj runtime.Object) error {
+    var pod *corev1.Pod
 
-	// mutate the fields in pod
+    log := logf.FromContext(ctx)
 
-	marshaledPod, err := json.Marshal(pod)
-	if err != nil {
-		return admission.Errored(http.StatusInternalServerError, err)
-	}
-	return admission.PatchResponseFromRaw(req.Object.Raw, marshaledPod)
-}
-```
+    d, ok := obj.(*corev1.Pod)
+    if !ok {
+        return fmt.Errorf("expected a Pod but got a %T", obj)
+    }
 
-If you need a client, just pass in the client at struct construction time.
+	// mutate the fields in pod
 
-If you add the `InjectDecoder` method for your handler, a decoder will be
-injected for you.
+    log.Info("Annotated pod")
 
-```go
-func (a *podAnnotator) InjectDecoder(d *admission.Decoder) error {
-	a.decoder = d
 	return nil
 }
 ```
@@ -59,7 +45,13 @@ you, you need to add markers. For example,
 Now you need to register your handler in the webhook server.
 
 ```go
-mgr.GetWebhookServer().Register("/mutate-v1-pod", &webhook.Admission{Handler: &podAnnotator{Client: mgr.GetClient()}})
+    if err := builder.WebhookManagedBy(mgr).
+        For(&corev1.Pod{}).
+        WithDefaulter(&podAnnotator{}).
+        Complete(); err != nil {
+        entryLog.Error(err, "unable to create webhook", "webhook", "Pod")
+        os.Exit(1)
+    }
 ```
 
 You need to ensure the path here match the path in the marker.