[Improvement] Allocate IPs for NodePort service to enable inner communication for multi-k8s

[loomts]

Is your improvement request related to a problem? Please describe. When implementing etcd add-on, NodePort service is OK for single k8s cluster. But in the scenario of multi-k8s, headless ClusterIP service will not useful, maybe need to allocate a list of IPs from Vars like what LoadBalancer service do.

Additional context Maybe it's not easy to allocate nodeIPs, not elegant method is to let user provide a list of static IPs?