added eos token for ppotrainer

[dame-cell]

What does this PR do?

Fixes 2387

• not sure if this works correctly ,might be missing some thing
• I added the use use_model_eos_token in the ppo_conifg.py to add kind of a way for the user to make configuration ,
  do we like this or just make it default with no configuration ?
• second do i need to write documentation since i added some new stuff to the config?

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• Did you write any new necessary tests?

Who can review?

@qgallouedec

[qgallouedec]

Maybe this line is enough? Why would we need two options?

[dame-cell]

I remove this line

elif hasattr(self.model.config, "eos_token_id") and self.args.use_model_eos_token:
    # Fallback to model config's EOS token
    self.model.generation_config.eos_token_id = self.model.config.eos_token_id

and kept the one which uses the tokenizer

I tested it locally and it seems to be doing fine the training was done perfectly with and without the eos_token_id
Do i need to like write custom tests or documentation ?