Kubeadm: Automate certificate copy between control planes in HA setups

- Joining control plane nodes to a HA cluster can now be simplified by enabling the optional automatic copy of certificates from an existing control plane node.
- You can now use `kubeadm init --experimental-upload-certs` and `kubeadm join --experimental-control-plane --certificate-key`.

configuration file, that gets forwarded to kubelet static pods to control pull policy for etcd and control plane images. This option allows for precise image pull policy specification for master nodes and thus for more tight control over images. It is useful in CI environments and in environments, where the user has total control over master VM templates (thus, the master VM templates can be preloaded with the required Docker images for the control plane services). ([#58960](https://github.com/kubernetes...

- HA improvements:
  - `kubeadm join --experimental-control-plane` can now be used to join control plane instances to an existing cluster.
  - `kubeadm upgrade node experimental-control-plane` can now be used for upgrading secondary control plane instances created with `kubeadm join --experimental-control-plane`.
Multi-arch support (EXPERIMENTAL):

- Restores priority of static control plane pods in the cluster/gce/manifests control-plane manifests ([#89970](https://github.com/kubernetes/kubernetes/pull/89970), [@liggitt](https://github.com/liggitt)) [SIG Cluster Lifecycle and Node]

### Other (Cleanup or Flake)

release.  A new alpha feature is introduced to improve the mechanism that nodes heartbeat back to the control plane.  The `NodeLease` feature results in the node using a `Lease` resource in the `kube-node-lease` namespace that is renewed periodically.  The `NodeStatus` that was used previously to heartbeat back to the control plane is only updated when it changes.  This reduces load on the control plane for large clusters. The Kubelet plugin registration mechanism, which enables automatic discovery...

  - The `kubeadm upgrade node config` and `kubeadm upgrade node experimental-control-plane` commands are deprecated in favor of `kubeadm upgrade node`, and will be removed in a future release. ([#78408](https://github.com/kubernetes/kubernetes/pull/78408), [@fabriziopandini](https://github.com/fabriziopandini))

  - Make "kubeadm upgrade apply" add the "node-role.kubernetes.io/control-plane" label on existing nodes that only have the "node-role.kubernetes.io/master" label during upgrade.
  - Please adapt your tooling built on top of kubeadm to use the "node-role.kubernetes.io/control-plane" label.
  - The taint applied to control-plane nodes "node-role.kubernetes.io/master:NoSchedule" is now deprecated and will be removed in a future release after a GA deprecation period.

`kubeadm` (N-3). This aligns with the recent change made by SIG Architecture that extends the support skew between the control plane and kubelets. Tolerate this new kubelet skew for the commands `init`, `join` and `upgrade`. Note that if the `kubeadm` user applies a control plane version that is older than the `kubeadm` version (N-1 maximum) then the skew between the kubelet and control plane would become a maximum of N-2. ([#120825](https://github.com/kubernetes/kubernetes/pull/120825), [@pacoxu](h...

### Deploy a more secure control plane with kubeadm

A new alpha feature allows running the kubeadm control plane components as non-root users. This is a long requested security measure in kubeadm. To try it you must enable the kubeadm-specific `RootlessControlPlane` feature gate. When you deploy a cluster using this alpha feature, your control plane runs with lower privileges.

- github.com/cncf/xds/go: [cb28da3 → e9ce688](https://github.com/cncf/xds/go/compare/cb28da3...e9ce688)
- github.com/envoyproxy/go-control-plane: [49ff273 → 9239064](https://github.com/envoyproxy/go-control-plane/compare/49ff273...9239064)
- github.com/envoyproxy/protoc-gen-validate: [v0.1.0 → v0.10.1](https://github.com/envoyproxy/protoc-gen-validate/compare/v0.1.0...v0.10.1)