Add path component to finalizer (#202)

The Kubernetes client warns about not having a path component in the
finalizer. This change adds a unqiue path component for each reconciler
kind.

internal/k8sutil/finalizer.go

@@ -0,0 +1,7 @@
+package k8sutil
+
+const NetbirdFinalizer = "finalizers.netbird.io"
+
+func Finalizer(kind string) string {
+	return NetbirdFinalizer + "/" + kind
+}