[docstring] Update `GPT2` and `Whisper` (#26642)
* [DOCS] Update docstrings for and tokenizer
* [DOCS] add pad_token argument to whisper tokenizer docstring
* [FIX] Reword pad_token description
* [CHORE] Apply style formatting
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Co-authored-by: jmcdonnell <jmcdonnell@fieldbox.ai>
