assistant2: Add button to open the prompt library (#23500)

This PR adds a button to open the prompt library from the configuration
view in Assistant2.

<img width="1309" alt="Screenshot 2025-01-22 at 5 38 08 PM"
src="https://github.com/user-attachments/assets/d514abca-53bc-4cde-bead-ab68a1994fb5"
/>

Release Notes:

- N/A