Use prod access endpoint first and fall back to the test endpoint when it's not available

[daxian-dbw]

PR Summary

Use prod access endpoint first and fall back to the test endpoint when it's not available. In this way, we can unblock the public preview without the prod endpoint being fixed, but also rely on the prod endpoint when it's fixed.

[NoriZC]

LGTM

[daxian-dbw]

The Copilot Access API uses standard HTTP status codes to indicate the success or failure of a request:

• 200 OK: The request was successful, and the response contains the authorization status.
• 401 Unauthorized: Common causes include missing tokens, invalid Object ID or Tenant ID, or incorrect audience claims.
• 403 Forbidden: The token lacks the required claims.
• 500 Internal Server Error: An unexpected error occurred on the server.

Even though we only saw 403 so far, I think it's safer to fall back to canary for other possible unsuccessful status code too, as we don't know what may happen when the prod endpoint is getting fixed for us.