**General background: **This is a back-end only ticket, but here is some context on the front-end:
* Private registrant usernames should be displayed to organizers
** Organizers should see some visual indicator of who is a private registrant. We are still determining what is the icon of choice, but it would be something like an eye that is crossed out next to the username of the private registrant.
** Private registrant usernames should not be displayed to non-organizers. Instead, non-organizers should just see the number of private registrants in the participant list (for example: "13 private registrations"). The reason why we want to display the number of private registrations is so that people don't think we have a bug in our code and miscalculated the number of registrants.
**Explanation of back-end work:**
Once the new schema is in place (T318120), we will need to change the backend code so that it supports the concept of private registration. Possible summary of the things to do:
- Add a boolean flag to the relevant method(s) in ParticipantsStore
- Add a private field + getter to the Participant class
- Add a fluent setter for this option to RegisterParticipantCommand
- Add the necessary logic to the backend code to allow private registration of participants
**Note**: this would not be exposed in the UI yet.