Add/Remove attendees to/from associated Talk room when changed via CalDAV

[ronnybremer]

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Is your feature request related to a problem? Please describe.
Yes. I originally opened a bug report but it turned out to be a missing feature. nextcloud/server#51212
When adding/removing attendees of a meeting through CalDAV, the attendee list in the associated Talk room is not updated, leading to inconsistencies between the two.

Describe the solution you'd like
Changed to the attendee list through CalDAV should be properly mirrored to the associated Talk room.

Describe alternatives you've considered
Manually updating the list of members in the Talk room shortly before the meeting starts.

Additional context
I am using the Mac OS X Calendar app to access the NC calendar, but I am pretty sure every CalDAV client would show the same result.

[nickvergessen]

This becomes especially tricky and a meeting is taking place in a conversation that otherwise existed already and is afterwards used/retained for other things.

I guess it would be possible nowadays a bit better with the conversation type "meeting" we added recently, what do you think @miaulalala