Support for conversion to next gen image formats (webp, jpeg2000 etc)

[shauunhimseelf]

Consider supporting next gen image formats
https://web.dev/uses-webp-images/

• Would suggest WebP as atm it looks like the one that will likely be the defacto standard
  Webp - Edge, Firefox, Chrome, partial safari
  JPEG2000 - Safari
  JPEG XR - IE

• We can automatically create each of the webp files on the CLI on fe build using

`for file in images/*; do cwebp -q 50 "$file" -o "${file%.*}.webp"; done`

(cwebp is shipped by default on Linux boxes)

• might be worth thinking if this is something we can wrap in the CDN stuff suggested in Support for html5 <picture> and srcset attributes  #164 particularly as this covers falling back where browsers dont support webp

[hellopablo]

Have looked into this before and it's on the mental list, thanks for recording it here.

My understanding is that browsers which support webp will send an accept header, which the server can sniff. It's also technically not important that .jpg files actually return a JPG. However, I think that we should redirect to the .webp if the browser supports it in case some in the middle cache caches a web thinking it's a jpg.

So:

• Browser: Give me file.jpg, btw I support webp
• Service: 302 to file.webp
• Browser: Give me file.webp

[shauunhimseelf]

Interesting side note, I think pagespeed does all this automatically (check the images on zehnder homepage - all webp under Chrome)