assistant2: Add context server list to configuration view (#27028)

This PR adds a context server list to the configuration view in
Assistant2:

<img width="1394" alt="Screenshot 2025-03-18 at 5 26 23 PM"
src="https://github.com/user-attachments/assets/58bf3920-1e35-4cb8-a32a-5ae9f98ce387"
/>

Release Notes:

- N/A

crates/assistant2/src/thread_store.rs

@@ -65,6 +65,10 @@ impl ThreadStore {
         Ok(this)
     }
 
+    pub fn context_server_manager(&self) -> Entity<ContextServerManager> {
+        self.context_server_manager.clone()
+    }
+
     /// Returns the number of threads.
     pub fn thread_count(&self) -> usize {
         self.threads.len()