Make binary-cache profile more generic

Change NGINX config of /profiles/binary-cache.nix to be more generic.

Example:

- virtualHosts."labs.cache.rnl.tecnico.ulisboa.pt" = {
+ virtualHosts.binary-cache = {
+     serverName = lib.mkDefault config.networking.fqdn;
      enableACME = true;

(Do not forget to change hosts)