scikit learn and gridsearch for hyperparameters + SHAP

[MariellaCC]

• experiment with https://scikit-learn.org/stable/modules/generated/sklearn.model_selection.GridSearchCV.html to see if there is a possibility to facilitate finetuning hyperparameters for users. The correct selection of hyperparameters can be crucial for the quality of the model/topics discovery, so this could be helpful. Impact on processing time needs to be assessed.

• See if there would be a possibility to use SHAP (https://shap.readthedocs.io/en/latest/index.html) and if this may bring useful insights to explain the modellling step