assistant2: Add docs to the notify_when_agent_waiting setting (#27622)

Release Notes:

- N/A

assets/settings/default.json

@@ -660,6 +660,7 @@
         }
       }
     },
+    // Shows a notification when the agent needs confirmation before running an edit tool call or when that's concluded.
     "notify_when_agent_waiting": true
   },
   // The settings for slash commands.