Support AVIF image format as an option

[franckc]

To improve both site load performance and SEO score we should add AVIF support. This is relevant for all our marketing sites:

• originprotocol.com
• ousd.com
• story.xyz

Notes:

• Some browsers do not support AVIF so we should provide a fallback like jpeg.
  Here is an article with an example of how to use the tag for that purpose.
• One complication comes from images uploaded via the CMS. We would need to modify the CMS to be able to provide 2 formats for an image (AVIF and jpg). Or use a service that does image conversion on the fly. For example CloudFlare image or https://imgix.com/