Add ability to choose multiple associated items (ie. courses) for the engagement

**Is your feature request related to a problem? Please describe.**
We now have the ability to select "all" for an engagement trigger, meaning any course/membership would match and trigger it. You can also select a single course. But if you want to select some, or select all but one, you can't.

**Describe the solution you'd like**
Add ability to choose multiple associated items (ie. courses) for the engagement, or items(s) to exclude if “All” is selected.