Provide calendar info from remote calendars via WebDAV

[janvlug]

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

Calendars that are subscriptions from link seem not to be available via WebDAV.

Example:
In Nextcloud Calendar subscribe to a calendar via a link:

1. Choose: New Calendar
2. Choose: New subscription from link (read only)
3. Enter for example: https://www.calendarlabs.com/ical-calendar/ics/101/Netherlands_Holidays.ics

Now open a client (like Thunderbird or Evolution) that is subscribed to the Nextcloud WebDAV.

Note that the newly added calendar from a link is not visible.

Describe the solution you'd like

I would like to see the calendars that are subscriptions from a link also in WebDAV clients, so that I do not have to add them manually on each client on each device.

Describe alternatives you've considered

No response

Additional context

No response

[tcitworld]

Duplicate of nextcloud/server#17754 (and see nextcloud/server#17754 (comment) for details).

Clients should be able to discover subscriptions collection themselves and allow to subscribe to them straight away, just like DAVx⁵ does. Otherwise it's really a hack.