[FEATURE] Add published flag for events

[mihail-varbanov]

Re: University Monday 2023/08/21 / 2023-08-23

2.1 We need a boolean flag for "Published". If this is false it should only appear for users who are the Admin or sub Admins of the event.

This is needed for the UIUC and Admi App/Web

4 Misho/Dobromir, when item 2.1 is ready above, in UIUC add a checkbox "Publish Event" and hook it up, in the Admin App hook it up.

Linked to rokwire/illinois-app#3623