Switch to webp as our main image format

[cjyabraham]

Since webp is going to be the default image type in WP 6.1 and is generally a smaller faster file type, let's see what we need to do to enable this across our sites in conjunction with the ShortPixel settings. Perviously I recall some issue deploying webp images due to Pantheon.

[thetwopct]

WP 6.1 is dropping the webP conversion. I think ShortPixel had the issues with webP on Pantheon. Could be cool to revisit, but not essential.