Feature Request: Make it configurable whether I share my system address book with trusted servers

Problem

As an administrator, I want to have a list of trusted servers so that users can collaborate on documents. I also want to create federated teams to make sharing easier.
However, I do not want the system address book to sync automatically, as this would result in me unnecessarily sharing personal data with all users across different environments, from a privacy and security standpoint.

As a user, I want to be able to collaborate with a few users in another environment via Federated Teams and Collaborative Document Editing.
However, I have no relationship with the majority of users in that other environment.
It is also undesirable to be able to see all individuals in my system address book from that other environment.

From a security perspective, I want to encourage collaboration but not share the personal data of all my users with other environments.

Proposal.

Make it configurable to sync a system address book between trusted servers.
I want to be able to configure trusted servers to create federated teams and support collaborative document editing.

In other words, add a configuration option to exchange sync tokens, but make it configurable to exchange the system address book.

The issue names federated teams, collaborative document editing, sync tokens, trusted servers, and system address book exchange, but it names no files or tests. Start by reviewing the existing trusted-server and sync-token configuration paths. Done means address-book sharing can be configured independently while federated collaboration continues to work.