Promtail: Add host label

nixos/modules/monitoring/exporters/promtail.nix

@@ -6,7 +6,12 @@
 #              exporters, but it is very similar in what it is doing -
 #              preparing local data and sending it off to a TSDB.
 
-{
+{ config, ... }:
+
+let
+  hostName = config.networking.hostName;
+
+in {
   config.services.promtail.enable = true;
   config.networking.firewall.interfaces.monitoringvpn.allowedTCPPorts = [ 9080 ];
   config.services.promtail.configuration = {
@@ -25,6 +30,7 @@
       journal = {
         labels = {
           job = "systemd-journal";
+          host = hostName;
         };
       };
       relabel_configs = [{