Add *kwargs to pass extra parameter to LGBMModel fit

[antoniocastelli1]

Dear PoweShap authors,

I am Antonio, Machine Learning Scientist @ Booking.com.
We found this package quite nice and useful. I have a question over the code:

powershap/powershap/shap_wrappers/shap_explainer.py

Line 245 in 4a60fbe

PowerShap_model.fit(X_train, Y_train, eval_set=(X_val, Y_val))

In this line the **kwargs are not passed to the fit method of LGBMModel. Since they are not passed it's not possible to set extra parameter to the fit method.
This means that the **kwargs and **fit_kwargs specified in PowerShap class initialization are not used.

Could you please check and maybe fix this in a new release.

Cheers

Antonio