add control-plane toleration (#122)

We're moving towards using the new control-plane toleration for rke2
addons. Adding control-plane for system-agent so it tolerates both
controlplane and control-plane similar to cluster-agent.

Author: kinarashah

manifests/system-upgrade-controller.yaml

@@ -68,6 +68,9 @@ spec:
         - key: "node-role.kubernetes.io/controlplane"
           operator: "Exists"
           effect: "NoSchedule"
+        - key: "node-role.kubernetes.io/control-plane"
+          operator: "Exists"
+          effect: "NoSchedule"
         - key: "node-role.kubernetes.io/etcd"
           operator: "Exists"
           effect: "NoExecute"