add cohen kappa in contrib.metrics module

[KickItLikeShika]

🚀 Feature

cohen's kappa is widely used in kaggle competitions, i think it would be great to add it in ignite.contrib.metrics

[vfdev-5]

@KickItLikeShika thanks for a FR, can you provide few links on where it is used etc.

Few links from our issues tracker :

• how to custom metric, such as kappa #551
• Add declarative trainer #924
  • https://github.com/Minyus/pipelinex/blob/master/src/pipelinex/extras/ops/ignite/metrics/cohen_kappa_score.py

[KickItLikeShika]

Competitions that use cohen's kappa for evaluation:

• https://www.kaggle.com/c/aptos2019-blindness-detection/overview/evaluation
• https://www.kaggle.com/c/petfinder-adoption-prediction/overview/evaluation

For more details about the Cohen's Kappa and Weighted Cohen's Kappa:

• https://www.real-statistics.com/reliability/interrater-reliability/weighted-cohens-kappa

[KickItLikeShika]

@vfdev-5 so what do you think? should i start working on it?

[vfdev-5]

@KickItLikeShika thanks for the links! How would you like to implement it ?

[KickItLikeShika]

I think just like average precision is implemented would be good, what do you think?

[vfdev-5]

OK, let's do like that