Add megatron-lm checkpoint eval support

[swag2198]

See details here: https://github.com/EleutherAI/lm-evaluation-harness?tab=readme-ov-file#megatron-lm-models

[geoalgo]

@swag2198 could you this issue with what you shared earlier today? (that we could run it on lm-eval and what remains to be done to integrate)

[swag2198]

Yes, I have a working solution with a custom venv and lm-eval , need to integrate it to the tool!

[swag2198]

I now have an integrated version in my branch here. It actually introduces quite a lot of changes, see the README here.