cgmanager: add module

nixos/modules/module-list.nix

···
   ./services/security/torify.nix
   ./services/security/tor.nix
   ./services/security/torsocks.nix
+  ./services/system/cgmanager.nix
   ./services/system/cloud-init.nix
   ./services/system/dbus.nix
   ./services/system/kerberos.nix

nixos/modules/services/system/cgmanager.nix

···
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.cgmanager;
+in {
+  meta.maintainers = [ maintainers.mic92 ];
+
+  ###### interface
+  options.services.cgmanager.enable = mkEnableOption "cgmanager";
+
+  ###### implementation
+  config = mkIf cfg.enable {
+    systemd.services.cgmanager = {
+      wantedBy = [ "multi-user.target" ];
+      after = [ "local-fs.target" ];
+      description = "Cgroup management daemon";
+      restartIfChanged = false;
+      serviceConfig = {
+        ExecStart = "${pkgs.cgmanager}/bin/cgmanager -m name=systemd";
+        KillMode = "process";
+        Restart = "on-failure";
+      };
+    };
+  };
+}