assistant: Require user to accept TOS for cloud provider (#16111)

This adds the requirement for users to accept the terms of service the
first time they send a message with the Cloud provider.

Once this is out and in a nightly, we need to add the check to the
server side too, to authenticate access to the models.

Demo:


https://github.com/user-attachments/assets/0edebf74-8120-4fa2-b801-bb76f04e8a17



Release Notes:

- N/A

crates/collab/src/db/tests.rs

@@ -10,6 +10,7 @@ mod extension_tests;
 mod feature_flag_tests;
 mod message_tests;
 mod processed_stripe_event_tests;
+mod user_tests;
 
 use crate::migrations::run_database_migrations;