Add progress bar component (#28518)

- Adds the progress bar component

Release Notes:

- N/A

crates/agent/src/ui.rs

@@ -1,5 +1,7 @@
 mod agent_notification;
 mod context_pill;
+mod user_spending;
 
 pub use agent_notification::*;
 pub use context_pill::*;
+// pub use user_spending::*;