[Feature] Expose RayCluster service annotations

[DmitriGekhtman]

Search before asking

• I had searched in the issues and found no similar feature requirement.

Description

There are situations in which a user may wish to modify the annotations set on the RayCluster service. So far we've seen this come up for these use-cases

• Setting up an NLB: [Bug] Head Node service is not getting exposed on Internal Load Balancer despite proper annotations #637
• Exposing Prometheus metrics: https://discuss.ray.io/t/exposing-kuberay-prometheus-metrics-configuration-on-head-service-annotations/7806/3

We should probably just add a spec.ServiceAnnotations field to the RayCluster CR.
That's a bit ugly, but it's harmless.

cc @kevin85421

Use case

Described above.

Related issues

There are some related issues, but I wanted to open a more targeted one.

https://discuss.ray.io/t/exposing-kuberay-prometheus-metrics-configuration-on-head-service-annotations/7806/3
#625
#648
#637

Are you willing to submit a PR?

• Yes I am willing to submit a PR!