code: func isControlPlane() bool {
  	filepath := kubeadmconstants.GetStaticPodFilepath(kubeadmconstants.KubeAPIServer, kubeadmconstants.GetStaticPodDirectory())
  	if _, err := os.Stat(filepath); os.IsNotExist(err) {
  		return false
  	}
  	return true
  }
docs: // isControlPlane checks if a node is a control-plane node by looking up
  // the kube-apiserver manifest file