Zoom: Option to create "Zoom participants" from registered event participans

This would be a one-off thing (possibly repeatable as long as we can easily know for who we already created a participant to just deal with new ones), probably via a button in the registrant list (for selected registrants) or on the videoconference page (for all registrants).

Clicking it would then create Zoom participants and email the individual join links to each person.

Start by tracing the registrant list and videoconference page, the two entry points suggested for this action. Determine how registered event participants and Zoom participants are represented, how existing participants can be identified, and how individual join links are emailed. Done means a repeatable action can create Zoom participants for selected or all registrants without duplicating existing ones and sends each person their join link.

Written by the indexing model from the issue text.