Automatically disable the system address book for large instances

[ChristophWurst]

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

As a Nextcloud admin I have to manually disable the system address book feature for my large installation because people are unable to use the Contacts app.

Describe the solution you'd like

Automatically detect that the instance exceeded x users and turn the SAB off. Allow me to turn it on if I like.

Describe alternatives you've considered

Finish nextcloud/contacts#3942.

Additional context
Add any other context or screenshots about the feature request here.

[ChristophWurst]

@SebastianKrupinski please backport this to stable31 (Hub 10)

[ChristophWurst]

This should also be noted in https://docs.nextcloud.com/server/latest/admin_manual/release_notes/upgrade_to_31.html so admins are not "surprised" by it.