Add regression evaluation metrics

[NickNtamp]

Additions:

• Regression evaluation metrics along with unit tests where added. The 3 more common metrics are there (r2, mse, mae)
• Regression model based on lgbm regressor was added. The r2 score is pretty low there but there are not many things we can do!
• LIME for regression was added
• Documentation was added along with the missing part for drifting metrics

Also closes: https://github.com/squaredev-io/administration/issues/422

[sinnec]

I'm done. I think @momegas or @stavrostheocharis should review this to judge on the whole picture!

[momegas]

Overall, this is great. I have some questions but most likely it will open to bigger discussions so lets not tackle them now. We can come back later.

Can we also have some notebook examples for regression models?

[NickNtamp]

Overall, this is great. I have some questions but most likely it will open to bigger discussions so lets not tackle them now. We can come back later.

Can we also have some notebook examples for regression models?

I am planning to have some but not under this ticket. I will add them in the notebooks roadmap ticket.