Allow additional labels on the RayCluster resource

[AdrianoKF]

I'm playing around with the combination of Kuberay and Kueue for quota management. In order to have Kueue manage the resource quotas for RayClusters, I need to put an additional label on the CR (not the head/worker pods; see the linked docs).

The current Helm chart unfortunately does not expose a way to do this easily, so I have to resort to helm template and manually add the label in the rendered manifest (I can't do kubectl label, either, since the admission controller apparently does not allow modifying the labels on an existing RayCluster CR).

Would it be possible to add a way in the Helm chart to pass extra labels to be applied to the RayCluster CR via values.yaml? I can provide a PR, if you are interested.