Auto generate avif and webp image formats

We could be dynamically generating the Avif and WebP images (instead of manually converting them) using the [Astro Images integration](https://docs.astro.build/en/guides/integrations-guide/image/). See the [documentation for the `@astrojs/images` Picture component](https://docs.astro.build/en/guides/integrations-guide/image/#responsive-pictures) for more info.