[avatar] Fix CORS for uiAvatar resolution

[vnphanquang]

fetch to uiAvatar failed with CORS, perhaps consider using picture tag for better native support and also much clearer interface / priority specification?

But if using picture tag, consider passing trials to slot for easy user customization?

[vnphanquang]

picture will not solve problem (as it does not pass to next source if resource is 404).

Root cause for cors error is ui-avatar endpoint does not allow cors if format is svg

Solution is to rely on image onerror and update src exhaustively.

Most helpful resource: https://stackoverflow.com/questions/52231187/handling-multiple-image-fallbacks-in-javascript