[FEATURE] Set event as favorite to an account by its NetId

[dobromirdobrev]

Is your feature request related to a problem? Please describe.

1. Events created via the admin API should be automatically favorited for the admins of the event. This is related to [USABILITY] My Events: Add Events you administer to the view illinois-app#4082 (comment) and https://github.com/rokwire/illinois_admin/issues/634
2. Private events that the users are registered to should be automatically be favorited for these users. This is related to: [USABILITY] Add "Guest List Only" Events to "My Events" for guest list  illinois-app#4213

Describe the solution you'd like
The backend and client teams to discuss the solution.