Add information about `Recently contacted` and `All contacts` address books

[DerDreschner]

Before You Submit

• I have checked for existing issues and pull requests related to my suggestion.
• I have posted on the Nextcloud Community Help Forum if my suggestion is a troubleshooting scenario or I'm unsure about the solution.

Type of Suggestion

Suggesting an improvement

Relevant Documentation Links

https://docs.nextcloud.com/server/stable/admin_manual/groupware/troubleshooting.html#contacts

Summary

In the troubleshooting guide, it should be mentioned where the Recently contacted and All contacts address books come from.

Details

During triage of nextcloud/contacts#3945, I realized that the troubleshooting section of the administration manual should mention where the Recently contacted and All contacts address books come from. It should also be mentioned how these can be removed/deactivated.

Additional Notes

No response