mT5 Support

[jlarson4]

Description

mT5 uses the same general architecture structure as T5, so adding support was trivial. I did discover a bug in the benchmarking for T5 models on transformers v5, which was also resolved in this PR

Fixes #912

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have not rewritten tests relating to key interfaces which would affect backward compatibility