Adding -> Configuration_flava.py
# What does this PR do?

Add configuration_flava.py to utils/documentation_tests.txt for doctest.

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

@sgugger could you please take a look at it?
Thanks =)
Hi @AShreyam 

This model config is done in #19724. Sorry if I forgot to follow this PR earlier. Going to close the PR though.
Thank you however.