Out of office events

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

This is most likely related to https://github.com/nextcloud/calendar/issues/39. As a user I would like to not only define my general availability via https://github.com/nextcloud/server/issues/27422 but also occasionally add entries to my calendar where I'm not around. This could be a vacation, doctor's visit or any other absence.

Right now I can only create an event and set myself as busy. For those who try to book an appointment it doesn't make much of a difference, I'm not there for both busy slots as well as out of office. Nevertheless it would be nicer to see a distinction between those two states.

Describe the solution you'd like

Similar to other email solutions there should not only be a New event but also New out of office or similar that lets me pick a block where others see me as unavailable.

Describe alternatives you've considered

Let the users create events as before but allow a third option for the free/busy state with Unavailable.

Additional context

This can be seen as part of https://github.com/orgs/nextcloud/projects/50

Start by reviewing the linked calendar issue, the general-availability issue, and the referenced project to determine the intended integration points. The work is done when users can create out-of-office periods or mark events unavailable and other users see that distinction when booking appointments.