Add rank correlation metrics

[kzkadc]

Description: added Spearman and Kendall rank correlation coefficient metrics.

https://en.wikipedia.org/wiki/Spearman%27s_rank_correlation_coefficient
https://en.wikipedia.org/wiki/Kendall_rank_correlation_coefficient

Check list:

• New tests are added (if a new feature is added)
• New doc strings: description and/or example code are in RST format
• Documentation is updated (if required)

[vfdev-5]

Thanks for the PR @kzkadc , I left few comments now about how to handle the imports of scipy in the code. I'll check the tests and docs a bit later, but overall implementation looks ok to me.

[vfdev-5]

Please also check code formatting, unit tests CI is also failed due to too long line

[vfdev-5]

LGTM, thanks for the PR @kzkadc !

[vfdev-5]

CI failures are unrelated, submitted a temporary fix with mlflow version constraints. Once #3278 is merged let's update this PR, rerun the CI and merge if all is green.