Resolve "Avatar URLs are wrong when using a CDN path and Object Storage"

What does this MR do?

Resolve a problem where if an avatar would be on remote storage and a CDN was configured, it would return an invalid URL.

Are there points in the code the reviewer needs to double check?

When everything will be migrated to object storage, I think we will be able to deprecate the CDN-specific code.

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #44775 (closed)

changelogs/unreleased/44775-avatar-on-os-fails-with-cdn.yml

+---
+title: Fixed wrong avatar URL when the avatar is on object storage.
+merge_request: 18092
+author:
+type: fixed