Automatically label robot nodes

[mkuf]

TL;DR

Robot nodes should automatically be labelled with

instance.hetzner.cloud/is-root-server: true

Expected behavior

The csi driver is using the label to prevent the node component to start on robot nodes, see
https://github.com/hetznercloud/csi-driver/blob/071d0e36c2abffcd92cf3d92dfe75babd33879a2/chart/values.yaml#L532-L540 for reference.

This label is not set automatically by the ccm and requires additional user intervention when adding robot nodes to the cluster.

The ccm should add this label automatically as it already knows which nodes are from the robot type and which are from the hcloud type.