Anonymous users cannot fetch agent avatar

[nickthecook]

I have configured an Agent in Onyx with a custom avatar. I've also set up anonymous chat.

Users who are not logged in can chat with the agent (expected), but they can't see the agent's avatar - it looks like a broken image in the browser.

Here's a curl command reproducing the issue:

$ curl 'https://example.com/api/persona/2/avatar' \
  -H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:154.0) Gecko/20100101 Firefox/154.0' \
  -H 'Accept: image/avif,image/webp,image/png,image/svg+xml,image/*;q=0.8,*/*;q=0.5' \
  -H 'Accept-Language: en-CA,en-US;q=0.9,en;q=0.8,fr-CA;q=0.7,fr;q=0.6' \
  -H 'Accept-Encoding: gzip, deflate, br, zstd' \
  -H 'Referer: https://example.com/app' \
  -H 'Connection: keep-alive' \
  -H 'Sec-Fetch-Dest: image' \
  -H 'Sec-Fetch-Mode: no-cors' \
  -H 'Sec-Fetch-Site: same-origin' \
  -H 'Priority: u=5, i' \
  -H 'Pragma: no-cache' \
  -H 'Cache-Control: no-cache'
{"detail":"Access denied. User is not authenticated."}

[nickthecook]

Anonymous users can fetch built-in avatars, but not avatars that the admin uploaded for the agent.

[modelpath-dev]

I'll work on this. Could you assign it to me?

I'll look at the current code, add a focused test, and send a small PR.