Add recommended actions to ClassImbalanceDataCheck

[angela97lin]

Post the epic to include recommended actions, we should address adding actions to the ClassImbalanceDataCheck to override AutoML's default behavior for handling data splitting.

[angela97lin]

Thoughts: How do we do this now, given that we've pulled the data check action work to all happen before automl search? The original idea was that we would change the data splitter for automl (via changing automl configs), but now we've completely separated actions from search.

[angela97lin]

Lower priority but we should come back and figure out how we can pass a automl config.