[kubernetes] Make worker version configurable

## What this PR does

The kubelet version of tenant k8s clusters is baked into the worker VM
image. Previously, selecting any version of tenant k8s had an impact
only on the controlplane, the workers were fixed at v1.33. This patch
modifies the KubeadmConfigTemplate to attempt to download the
user-selected versions of kubelet and kubeadm and replace the baked-in
versions with those. If failing, the bootstrap continues with the
baked-in versions.

### Release note

```release-note
[kubernetes] Make kubelet versions on tenant k8s clusters' worker nodes
user-configurable.
```

Signed-off-by: Timofei Larkin <lllamnyp@gmail.com>

packages/apps/kubernetes/templates/cluster.yaml

@@ -182,6 +182,33 @@ metadata:
 spec:
   template:
     spec:
+      files:
+      - path: /usr/bin/update-k8s.sh
+        owner: root:root
+        permissions: "0755"
+        content: |
+          #!/usr/bin/env bash
+          set -euo pipefail
+
+          # Expected to be passed in via preKubeadmCommands
+          : "${KUBELET_VERSION:?KUBELET_VERSION must be set, e.g. v1.31.0}"
+
+          ARCH="$(uname -m)"
+          case "${ARCH}" in
+            x86_64) ARCH=amd64 ;;
+            aarch64) ARCH=arm64 ;;
+          esac
+
+          # Use your internal mirror here for real-world use.
+          BASE_URL="https://dl.k8s.io/release/${KUBELET_VERSION}/bin/linux/${ARCH}"
+
+          echo "Installing kubelet and kubeadm  ${KUBELET_VERSION} for ${ARCH}..."
+          curl -fsSL "${BASE_URL}/kubelet" -o /root/kubelet
+          curl -fsSL "${BASE_URL}/kubeadm" -o /root/kubeadm
+          chmod 0755 /root/kubelet
+          chmod 0755 /root/kubeadm
+          if /root/kubelet --version ; then mv /root/kubelet /usr/bin/kubelet ; fi
+          if /root/kubeadm version ; then mv /root/kubeadm /usr/bin/kubeadm ; fi
       diskSetup:
         filesystems:
         - device: /dev/vdb
@@ -205,6 +232,7 @@ spec:
         {{- end }}
       {{- end }}
       preKubeadmCommands:
+      - KUBELET_VERSION={{ include "kubernetes.versionMap" $}} /usr/bin/update-k8s.sh || true
       - sed -i 's|root:x:|root::|' /etc/passwd
       - systemctl stop containerd.service
       - mkdir -p /ephemeral/kubelet /ephemeral/containerd