[Core] Add ray-start option 'session-name'

[enori]

Why are these changes needed?

Currently, the session name for a ray cluster is set to session_{timestamp}_{pid} (documentation), which is hard to retrieve/predict. We want to provide users the Grafana metrics for their KubeRay ray cluster, but we don't know what the SessionName label filter should be set to. If we can customize the session name as a command-line argument to ray start, we can generate a unique name and pass it to the Kuberay as RayStartParams. Then, we can easily filter the prometheus metrics with this name.

Related issue number

#46281

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    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
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• Testing Strategy
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[can-anyscale]

need review from core folks