modules/nixos: add cgroups and exporter

modules/nixos/ci-builder.nix

@@ -1,3 +1,32 @@
 {
-  imports = [ ../shared/ci-builder.nix ];
+  config,
+  inputs,
+  pkgs,
+  ...
+}:
+{
+  imports = [
+    ../shared/ci-builder.nix
+    inputs.cgroup-exporter.nixosModules.default
+  ];
+
+  services.prometheus.exporters.cgroup.enable = true;
+
+  services.telegraf.extraConfig.inputs.prometheus.urls = [
+    "http://localhost:${toString config.services.prometheus.exporters.cgroup.port}/metrics"
+  ];
+
+  nix = {
+    package = pkgs.nixVersions.nix_2_25;
+
+    settings = {
+      experimental-features = [
+        "auto-allocate-uids"
+        "cgroups"
+      ];
+
+      auto-allocate-uids = true;
+      use-cgroups = true;
+    };
+  };
 }