add prometheus node exporter

prometheus.nix

@@ -0,0 +1,12 @@
+{ config, pkgs, ... }:
+
+{
+  networking.firewall.allowedTCPPorts = [ 9100 ];
+  services.prometheus.exporters.node = {
+    enable = true;
+    port = 9100;
+    enabledCollectors = [ "systemd" ];
+    extraFlags = [ "--collector.ethtool" "--collector.softirqs" "--collector.tcpstat" "--collector.wifi" ];
+  };
+}
+