[Doctest] Add configuration_m2m_100.py
Add configuration_m2m_100.py to utils/documentation_tests.txt for doctest.

Based on issue https://github.com/huggingface/transformers/issues/19487

@ydshieh can you please have a look? thanks :D

it passes the test with a few warnings.
_The documentation is not available anymore as the PR was closed or merged._<|||||>Thank you for your assistance @ydshieh 😃