[Serve] Modify max_concurrency in actor options to respect max_ongoing_requests (#47681)

[akyang-anyscale]

Why are these changes needed?

This PR modifies the actor_options used when deploying replicas. Deployment will use the configured max_ongoing_requests attribute of the deployment config as the replica's max_concurrency if
the concurrency is not explicitly set. This is to prevent replica's max_concurrency from capping
max_ongoing_requests.

Related issue number

Closes #47681

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