This issue is based on the following comment:
could we use a Pipeline instead of get_dummies? See #649

Originally posted by @adrinjalali in #614 (comment)

Using a Pipeline with all the preprocessing steps is cleaner and a better practice. However, we currently can't pass a Pipeline to mitigation techniques since they run check_X_y internally. If there are preprocessing steps, they are not executed before this check and we get a failure.

Goals

• use Pipeline in examples, tests, etc. (we have several places with get_dummies which are almost identical
• fix mitigation technique behavior to work with Pipelines that include preprocessing steps
• stretch goal (perhaps out of scope for the initial PR): make it possible to pass our mitigation techniques to Pipelines.