Add new sklearn feature to classification chapter

Add example for using sklearn.inspection.DecisionBoundaryDisplay.

changed milestone to %Organisation for the 5th workshop (Sep 2022)

assigned to @oschmanf

I checked the DecisionBoundaryDisplay. Default settings are quite "ugly" and tuning it to look good is a similar effort as done in plot_decision_surface function.

I'm in favor of not changing our code, but still mention DecisionBoundaryDisplay in the script.

@schmittu Thank you for looking into this. Then I will continue to use plot_decision_surface and just briefly mention DecisionBoundaryDisplay.

created branch 69-add-new-sklearn-feature-to-classification-chapter to address this issue

mentioned in merge request !51 (merged)

created branch 69-add-new-sklearn-feature-to-classification-chapter-2 to address this issue

mentioned in commit ea4a5fdf

closed with merge request !51 (merged)

mentioned in commit 1c6f63b4