Branched off of #2204. #2204 is about compressing on the fly and this is about providing precompressed versions of static files so that 1) Caddy doesn't have to encode each response and 2) so that we can use Brotli.

What this involves would probably depend on the type of deployment. E.g. for Docker images, we'd have to perform the precompression when building them.

For context, PR implementing #2204: #2410.