[FT] Add Gemba MQM Translation Metric

[JoelNiklaus]

Issue encountered

The metrics only include rather outdated translation metrics.

Solution/Feature

Gemba MQM seems to be a current metric. Adding it would make translation evaluation better.

[NathanHB]

Looks nice ! This is using external APIs and does not seem to have a PyPI package so we would need to implement it in Lighteval. This not not high priority but if you need it feel free to open a PR and we can help you set it up :)

[JoelNiklaus]

Great, thanks!
Yes, I see two avenues:

1. Fork their repo, publish a pip package and integrate it like that.
2. Just copy their prompts and post processing functions.

IMO option 1 is cleaner and also allows other people to use the metric more easily.

@chuandudx Would you be interested in taking this?

[JoelNiklaus]

This is done: I forked the repo (https://github.com/joelniklaus/gemba) and deployed it to pypi (https://pypi.org/project/gemba/). I also included it in PR #389. We can also think about pulling some metrics from this PR to the metrics_sample so everyone can use them afterwards.