kubeadm: clarify the usage of kubeadm commands in our external etcd guide (#17541)

content/en/docs/setup/production-environment/tools/kubeadm/setup-ha-etcd-with-kubeadm.md

@@ -8,6 +8,14 @@ weight: 70
 
 {{% capture overview %}}
 
+{{< note >}}
+While kubeadm is being used as the management tool for external etcd nodes
+in this guide, please note that kubeadm does not plan to support certificate rotation
+or upgrades for such nodes. The long term plan is to empower the tool
+[etcdadm](https://github.com/kubernetes-sigs/etcdadm) to manage these
+aspects.
+{{< /note >}}
+
 Kubeadm defaults to running a single member etcd cluster in a static pod managed
 by the kubelet on the control plane node. This is not a high availability setup
 as the etcd cluster contains only one member and cannot sustain any members