Closes #2538 Works as expected on latest Firefox and Chromium.
See https://github.com/cdr/code-server/pull/2383#issuecomment-738024951
I took our website's SVG favicon and plopped it on a round white rectangle in Affinity Designer. The I exported it as an SVG and wrote a script that uses imagemagick to convert to the various sizes and formats we need. Closes #2307
