DNS resolvers on NixOS / Guix

[aither64]

DNS resolvers configured from vpsAdmin are set on containers using osctl ct set dns-resolver and osctld will generate /etc/resolv.conf on container start or on change. Guix in default configuration doesn't seem to mind and doesn't touch /etc/resolv.conf. NixOS however either uses resolvconf to generate /etc/resolv.conf or expects etc.environment."resolv.conf". In any case, it overrides settings from vpsAdmin. NixOS template thus sets networking.nameservers to cloudflare DNS, which works, but it is a pity to not to use our own resolvers at vpsFree.cz when we could.