Steps to reproduce:
1. Populate Opencast with a large number of internal users (say 5000)
2. Create a new Event
The Create Event dialog is slow to load and editing the Presenters and Contributors fields is unwieldy.
The /admin-ng/event/new/metadata REST endpoint includes the entire set of available users in the JSON response, in the collection for EVENTS.EVENTS.DETAILS.METADATA.PRESENTERS and EVENTS.EVENTS.DETAILS.METADATA.CONTRIBUTORS
Workaround (if any):