flatcar: Set cloud-provider kubelet flag to "external"

In-tree cloud provider support was removed in k8s v1.27.

See the following:

- kubernetes/kubernetes#118899
- kubernetes/kubernetes#115838
- #4301

Signed-off-by: Johanan Liebermann <jliebermann@microsoft.com>

templates/cluster-template-flatcar.yaml

@@ -45,19 +45,19 @@ spec:
       nodeRegistration:
         name: $${COREOS_EC2_HOSTNAME}
         kubeletExtraArgs:
-          cloud-provider: aws
+          cloud-provider: external
     clusterConfiguration:
       apiServer:
         extraArgs:
-          cloud-provider: aws
+          cloud-provider: external
       controllerManager:
         extraArgs:
-          cloud-provider: aws
+          cloud-provider: external
     joinConfiguration:
       nodeRegistration:
         name: $${COREOS_EC2_HOSTNAME}
         kubeletExtraArgs:
-          cloud-provider: aws
+          cloud-provider: external
     format: ignition
     ignition:
       containerLinuxConfig:
@@ -138,7 +138,7 @@ spec:
       joinConfiguration:
         nodeRegistration:
           kubeletExtraArgs:
-            cloud-provider: aws
+            cloud-provider: external
           name: $${COREOS_EC2_HOSTNAME}
       format: ignition
       ignition: