Discuss about compile config

After #5581, torch dynamo can be enabled by engine.compile and there's no longer a config for that, which simplify things a lot.

Internally, we are primarily supporting a few models, specifically LLaMA and its variants. To minimize user effort, we aim to:

1. Automatically set leaf modules: For example, LlamaDecoderLayer for LLaMA.
2. Adjust prefetch arguments: Optimize prefetch settings when dynamo is enabled (max_live_parameters and prefetch_bucket_size to be specific)

Previously, in DeepSpeed, we could detect if dynamo was enabled via ds_config, allowing us to apply these adjustments seamlessly. However, with the recent changes, it is now challenging to determine if dynamo is enabled during the ds_init phase.

To solve that, IMO there're several options:

1. just warn when dynamo is enabled later and the tuning I mentioned is not enabled, ask the user to change their code/config
2. introduce new args/envs for that
3. do that in upper layer frameworks e.g. https://github.com/oraluben/transformers/commit/7f18b1cc7b855059c8c0344290ebae96115649df and https://github.com/oraluben/accelerate/commit/113df582b266ffa929cd7ca75241aa0e5caa4212

We're currently migrating from option 2 to option 3, for that's easy to maintain and add less ad-hoc logic in deepspeed. We'd like to know your options here, not limited to if you think this is a good idea overall, what do you think is the best way to implement, would you like to get this upstreamed.

Thanks!

@tohtana @loadams cc @SunMarc @tjruwase