Group organizers can't promote an event attendee to event host

A group organizer has no way to promote an event attendee to event host (co-host). There is no action to make an existing attendee a host of the event. **Expected:** A group organizer should be able to promote an attendee of one of the group's events to event host / co-host. **Where:** Event attendees / management — for an event belonging to a group the user organizes. **Steps to reproduce:** 1. As a group organizer, open one of the group's events 2. View the attendees / RSVP list 3. There is no option to promote an attendee to event host