Deprecated option optimize_cuda_cache warning on import of trl

[ChanderG]

When you just import trl, we get the following warning:

$ python3
Python 3.10.8 (main, Nov 24 2022, 14:13:03) [GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import trl
/opt/conda/lib/python3.10/site-packages/trl/trainer/ppo_config.py:141: UserWarning: The `optimize_cuda_cache` arguement will be deprecated soon, please use `optimize_device_cache` instead.
  warnings.warn(

Unless this is left on purpose, I believe that this line https://github.com/huggingface/trl/blob/main/trl/trainer/ppo_config.py#L107, should be changed from:

optimize_cuda_cache: bool = False

to:

optimize_cuda_cache: Optional[bool] = None

to get rid of the warning.

I can open a PR if this warning is not needed on default config creation.

[lvwerra]

Indeed, that's correct! A PR would be great, thank you!