Make Talk converstations opt-out

[ChristophWurst]

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

As a Nextcloud Calendar user I have to click Create a talk room for new appointment configs so that a Talk room is created.

Describe the solution you'd like

Check the checkbox by default. User who don't want this can uncheck the checkbox.

Describe alternatives you've considered

N/a

Additional context

Requested by @jancborchardt

[tcitworld]

This looks like a big change and might generate a lot of Talk rooms for nothing. Make sure to have at least an appconfig option to toggle this default value.