[Serve] Support callables in `serve.batch` args

[Yard1]

Why are these changes needed?

This PR allows for callables to be used in serve.batch arguments, allowing users to add logic to dynamically change the max batch size and timeout. It also makes batch_queue_cls configurable as an advanced API.

Related issue number

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• [ ] I've included any doc changes needed for https://docs.ray.io/en/master/.
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• Testing Strategy
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[edoakes]

@Yard1 would you mind adding a short extension to https://docs.ray.io/en/latest/serve/tutorials/batch.html showing how to do this?

[edoakes]

As discussed offline, let's go with "magic" instance variable names for now:

• __ray_serve_max_batch_size
• __ray_serve_batch_wait_timeout_s