[BugFix] TRL distillation bug fix

[horheynm]

SUMMARY:
Bug fix for

0/test_example_scripts_ex_trl_co0/examples/trl_mixin/sft_trainer.py", line 15, in _init\n    super().init(*args, **kwargs)\nTypeError: SessionManagerMixIn.init_() missing 1 required positional argument: \'dataset_args\'\n').returncode

Solution is to revert the dataset args to optional back again

TEST PLAN:
Pass script run

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