Consider using URLs to assets that are unique per version

[rwinch]

Instead of having an asset of site.css perhaps we could use something like site-{checksum}.css or site-{git-sha1}.css This would ensure we didn't need to bust caches.

Alternatively we could potentially write the links using something like: site.css?v={checksum} or site.css?v={git-sha1}. The advantage of this approach is it would likely be very easy since we already include the git version for antora-ui-version and we would just need to place @@antora-ui-version in the templates next to any existing URLs. The disadvantage is that we may be moving our hosting platform which I'm not sure if it supports query strings on assets.