assistant2: Add headers to chat messages (#11191)

This PR adds headers to the chat messages in the new assistant panel.

Adapted from the work on the `assistant-chat-ui` branch.

Release Notes:

- N/A
ae650342ceMarshall Bowers committed on 4/29/2024, 10:21:43 PM· committed by GitHubparent1c09b69
3 files changedLine totals unavailable