nixos/k3s: add to environment.systemPackages for adminstration

nixos/modules/services/cluster/k3s/default.nix

@@ -81,6 +81,8 @@ in
     # supporting it, or their bundled containerd
     systemd.enableUnifiedCgroupHierarchy = false;
 
+    environment.systemPackages = [ config.services.k3s.package ];
+
     systemd.services.k3s = {
       description = "k3s service";
       after = mkIf cfg.docker [ "docker.service" ];