fix(k0s): only include workers in autopilot if there are any

bootstrap/templates/kubernetes/apps/system-upgrade/k0s/app/plan.yaml.j2

@@ -18,6 +18,8 @@ spec:
           controllers:
             discovery:
               selector: {}
+          {% if cluster.nodes.inventory | selectattr('controller', 'equalto', False) | list | length %}
           workers:
             discovery:
               selector: {}
+          {% endif %}