text: Title: automate detection of classifier and regressor for tree based transformers
  Body: At the moment, in the categorical tree encoder and the tree discretiser, we have an argument is_regression that the user needs to fill in in order to detect if the user is aiming to perform classification or regression.
  
  Sklearn has an automated process with the is_classification (see Decision tree source code).
  
  Can we bring this functionality to feature-engine?
  
  I think we can :p