nixos/tailscale-derper: drop nginx upstream to improve reliability (#377640)

    services = {

      nginx = {

        enable = true;

        upstreams.tailscale-derper = {

          servers."127.0.0.1:${toString cfg.port}" = { };

          extraConfig = ''

            keepalive 64;

          '';

        };

        virtualHosts."${cfg.domain}" = {

          addSSL = true; # this cannot be forceSSL as derper sends some information over port 80, too.

          locations."/" = {

            proxyPass = "http://tailscale-derper";

            proxyPass = "http://127.0.0.1:${toString cfg.port}";

            proxyWebsockets = true;

            extraConfig = ''

              keepalive_timeout 0;