Implement coderd list modules endpoint

1. Import the response type from coder-registry
2. In handler make request to registry list module api endpoint
3. Parse into the registry response struct
4. Return to the frontend
5. Handle errors properly as a reverse proxy (make sure we don't accidentally throw any 500s we don't want)

Start at the coderd handler for the list modules endpoint and identify the request path to the registry list module API. Read the coder-registry response type and trace how the handler returns data to the frontend. Done means the response is parsed and proxied correctly, with errors handled without unintended 500 responses.

Scritto dal modello di indicizzazione a partire dal testo della issue.