We need to set up ETag hashing manually as Caddy defaults to using the
modified time on files and gives up when it sees the weird times Nix has
set all the files to to preserve reproducibility.

This involved both switching to the new git remote and passing the
resolved git commit as an environment variable to the server.

Shouldn't need to do this when I'm running my own instance as I'm not a
service provider so not subject to the OSA.

This allows me to use a more recent version of jj that defaults to using
change id headers.

I think I inadvertently formatted every file on my system whilst adding
this change :(

This was enough configuration to get my site building and serving from a
Hetzner VPS instance!