Add arguments to pass Ray cluster head and worker templates

[astefanutti]

Issue link

Fixes #413.

What changes have been made

This PR adds parameters to the Ray cluster configuration API, so users can provide Pod template for the head and worker nodes, e.g.:

from kubernetes import V1PodTemplateSpec, V1PodSpec, V1Toleration

cluster = Cluster(ClusterConfiguration(
    worker_template=V1PodTemplateSpec(
        spec=V1PodSpec(
            tolerations=[V1Toleration(
                key="nvidia.com/gpu",
                operator="Exists",
                effect="NoSchedule",
            )],
            node_selector={
                "nvidia.com/gpu.present": "true",
            },
        )
    ),
    head_template=V1PodTemplateSpec(...),
))

Verification steps

Checks

• [ ] I've made sure the tests are passing.
• Testing Strategy
  • [ ] Unit tests
  • [ ] Manual tests
  • [ ] Testing is not required for this change

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[openshift-merge-robot]

PR needs rebase.

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