Add support for Avif Images

[rustyconover]

Hi Team,

Doing more testing today it seems there should be support added for Avif format images.

https://caniuse.com/avif

Thanks,

Rusty

[papandreou]

I know that we have specific Asset subclasses for a bunch of image and font types, but we should be falling back to a generic Asset when we don't know the specific Content-Type or file extension. In this case it means that we don't recognize it as a bitmap image type, but basic things like bringhome shouldn't care about that, since bitmap images generally don't have outgoing relations.

We can easily add Avif as an asset type, but I'm curious how exactly you're seeing it break?