[Doctest] Add `wav2vec2_conformer.py`
Add `configuration_wav2vec2_conformer.py` to `utils/documentation_tests.txt` for doctest.

Based on issue: [19487](https://github.com/huggingface/transformers/issues/19487)

@ydshieh could you please check it? If it is ok for you I can keep working on the "wav2vec2" ones!
Thank you very much for your support :)
_The documentation is not available anymore as the PR was closed or merged._<|||||>Hi @juancopi81 Wav2Vec2 is already done.
See [documentation_tests.txt](https://github.com/huggingface/transformers/blob/main/utils/documentation_tests.txt) on the main branch. You can work on other model configs if you would like to 🤗 <|||||>Great! Thanks a lot @ydshieh 🤗 