prometheus-node-exporter service: update for new arguments handling

The behaviour have changed again. Listed collectors are now enabled in
addition to the default one.

Also run as DynmicUser instead of user nobody as the exporter doesn't need
any state.

nixos/modules/services/monitoring/prometheus/node-exporter.nix

@@ -33,7 +33,7 @@ in {
         default = [];
         example = ''[ "systemd" ]'';
         description = ''
-          Collectors to enable. Only collectors explicitly listed here will be enabled.
+          Collectors to enable. The collectors listed here are enabled in addition to the default ones.
         '';
       };
 
@@ -64,13 +64,12 @@ in {
       wantedBy = [ "multi-user.target" ];
       script = ''
         exec ${pkgs.prometheus-node-exporter}/bin/node_exporter \
-          ${optionalString (cfg.enabledCollectors != [])
-            ''-collectors.enabled ${concatStringsSep "," cfg.enabledCollectors}''} \
-          -web.listen-address ${cfg.listenAddress}:${toString cfg.port} \
+          ${concatMapStrings (x: "--collector." + x + " ") cfg.enabledCollectors} \
+          --web.listen-address ${cfg.listenAddress}:${toString cfg.port} \
           ${concatStringsSep " \\\n  " cfg.extraFlags}
       '';
       serviceConfig = {
-        User = "nobody";
+        DynamicUser = true;
         Restart  = "always";
         PrivateTmp = true;
         WorkingDirectory = /tmp;