Add support for defining labels for node groups utilising the label selector API

[juzerpatanwala]

Ray has a Label Selector API which allows trainings to run on specific worker groups based on the labels assigned to the worker groups in the Ray runtime environment. The ray-cluster helm chart doesn't have the functionality to add the top-level labels field inside headGroupSpec and workerGroupSpecs

Ref - https://docs.ray.io/en/latest/cluster/kubernetes/user-guides/label-based-scheduling.html#overview