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/migrations.sqlite/20221109000000_test_schema.sql

@@ -9,7 +9,8 @@ CREATE TABLE "users" (
     "connected_once" BOOLEAN NOT NULL DEFAULT false,
     "created_at" TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
     "metrics_id" TEXT,
-    "github_user_id" INTEGER
+    "github_user_id" INTEGER,
+    "accepted_tos_at" TIMESTAMP WITHOUT TIME ZONE
 );
 CREATE UNIQUE INDEX "index_users_github_login" ON "users" ("github_login");
 CREATE UNIQUE INDEX "index_invite_code_users" ON "users" ("invite_code");