AVIF by default in image services

[re-xyr]

Body

Summary

Now that AVIF is baseline, it makes sense to switch to AVIF as the default format for image services.

Background & Motivation

Caniuse says AVIF is supported by 93.98% of browsers globally. This is only 1.42% off from WebP's 95.4%.

Local images in markdown files can only use the default image format. This change will make all markdown pages use the more efficient AVIF format without needing to switch to MDX and using the <Picture /> component.

In terms of required changes, as far as I can tell, we only need to change one line.

Goals

• Use the most efficient baseline-available image format by default.

[jasikpark]

In terms of required changes, as far as I can tell, we only need to change one line.

Make the PR, let's get this going, I'm excited to drop my pnpm patch of astro 😁

[Princesseuh]

AVIF is baseline, but it takes a very long time to encode compared to Webp so imo it's suboptimal as a default still