Fix sidecar injection when pod annotations is nil. (#250)

When a pod does not have any annotations the injector will fail. This
change adds a test for the case and also fixes the issue.

Fixes #246

Signed-off-by: Philip Laine <philip.laine@gmail.com>

internal/webhook/v1/pod_webhook.go

@@ -172,6 +172,9 @@ func (d *PodNetbirdInjector) Default(ctx context.Context, pod *corev1.Pod) error
 		return fmt.Errorf("unknown injection mode %s", sidecarProfile.Spec.InjectionMode)
 	}
 
+	if pod.Annotations == nil {
+		pod.Annotations = map[string]string{}
+	}
 	pod.Annotations[SidecarProfileAnnotation] = sidecarProfile.Name
 
 	return nil