bakery: add kubernetes sysext helper

[tormath1]

How to use

./create_kubernetes_sysext.sh 1.27.3 kubernetes then

variant: flatcar
version: 1.0.0
storage:
  files:
    - path: /opt/extensions/kubernetes.raw
      mode: 0644
      contents:
        source: http://.../kubernetes.raw
  links:
    - path: /etc/extensions/kubernetes.raw
      hard: false
      target: /opt/extensions/kubernetes.raw

Tests

• Tested on QEMU (simply deploy a control plane)

• Tested on OpenStack CAPI (CAPO) with the following template diff:

+            storage:
+              files:
+                - path: /opt/extensions/kubernetes.raw
+                  mode: 0644
+                  contents:
+                    remote:
+                      url: https://storage.googleapis.com/tormath1-flatcar/kubernetes.raw
+              links:
+                - filesystem: root
+                  path: /etc/extensions/kubernetes.raw
+                  hard: false
+                  target: /opt/extensions/kubernetes.raw
             systemd:
               units:
               - name: [email protected]
@@ -106,6 +118,18 @@ spec:
     ignition:
       containerLinuxConfig:
         additionalConfig: |
+          storage:
+            files:
+              - path: /opt/extensions/kubernetes.raw
+                mode: 0644
+                contents:
+                  remote:
+                    url: https://storage.googleapis.com/tormath1-flatcar/kubernetes.raw
+            links:
+              - filesystem: root
+                path: /etc/extensions/kubernetes.raw
+                hard: false
+                target: /opt/extensions/kubernetes.raw
           systemd:
             units:
             - name: [email protected]

On the node:

$ systemd-sysext status
HIERARCHY EXTENSIONS SINCE
/opt      none       -
/usr      kubernetes Mon 2023-07-24 16:01:05 UTC

Nodes:

$  kubectl --kubeconfig=./${CLUSTER_NAME}.kubeconfig get nodes
NAME                                  STATUS   ROLES           AGE     VERSION
capi-quickstart-control-plane-c5lkk   Ready    control-plane   7m34s   v1.27.3
capi-quickstart-md-0-hdsf5            Ready    <none>          6m55s   v1.27.3
capi-quickstart-md-0-kjj9m            Ready    <none>          6m56s   v1.27.3
capi-quickstart-md-0-qdbcn            Ready    <none>          6m56s   v1.27.3
$ kubectl get kubeadmcontrolplane
NAME                            CLUSTER           INITIALIZED   API SERVER AVAILABLE   REPLICAS   READY   UPDATED   UNAVAILABLE   AGE     VERSION
capi-quickstart-control-plane   capi-quickstart   true          true                   1          1       1         0             8m53s   v1.27.2