Option to disable/enable the system address book from the admin settings UI

[ChristophWurst]

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

As a Nextcloud admin I want to disable/enable the system address book. I can only do this via occ: https://docs.nextcloud.com/server/latest/admin_manual/groupware/contacts.html#system-address-book.

Describe the solution you'd like

Offer an admin settings UI option to toggle this setting.

Describe alternatives you've considered

N/a

Additional context

Right now admins can't disable the SAB. With #49431 admins might want to enable it.