Propagate birthday events from system address book to each user's birthday calendar

⚠️ This issue respects the following points: ⚠️ • This is a bug, not a question or a configuration/webserver/proxy issue. • This issue is not already reported on [Github]( OR [Nextcloud Community Forum]( _(I've searched it)_. • Nextcloud Server is up to date. See [Maintenance and Release Schedule]( for supported versions. • I agree to follow Nextcloud's [Code of Conduct]( Bug description the birthday calendar does not use the dates of birth stored by the users. Only manually created contacts and their dates of birth appear in the birth calendar. Steps to reproduce 1. User stores his date of birth in the personal settings 2. User 2 then activates the birthday calendar 3. Birth dates are not displayed Expected behavior the birthday calendar should use the data from all address books. So the self-created contacts and especially the system contacts which are located in the system address book, which contains all accounts. Nextcloud Server versio…