[red-knot] Add settings support to playground (#16929)
## Summary
This PR extends the Red Knot playground by adding configuration support
by adding a `knot.json` file.
<img width="1679" alt="Screenshot 2025-03-23 at 21 12 16"
src="https://github.com/user-attachments/assets/81ff1588-a07a-4847-97d8-61250aa2feda"
/>
