Appointments : Add support for Ical calendars

[fccl-vandoeuvre]

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

Hello,

We'd like to enable our employees to use the appointments function in Nextcloud's Calendar app, but calendar management is currently centralized in the Zimbra email client.

To do this, we need to use the “Additional calendars to check for conflicts” function. However, this function must be able to handle calendars loaded into Nextcloud in ICS (it's not possible to load calendars from other servers into CalDav), which doesn't seem to be the case at present.

Sincerely, Axel.

Describe the solution you'd like

Is it possible to enable support for these Icalendar calendars, or is there a technical limitation?

Describe alternatives you've considered

No response

Additional context

No response