add kubectl and helm

kubernetes-helm/default.nix

@@ -0,0 +1,20 @@
+{ dockerTools
+, cacert
+, kubernetes-helm
+}:
+dockerTools.buildImage {
+  inherit (kubernetes-helm) name;
+
+  contents = [
+    cacert
+    kubernetes-helm
+  ];
+
+  config = {
+    Entrypoint = [ "/bin/helm" ];
+    Env = [
+      "PATH=/bin"
+      "SSL_CERT_FILE=${cacert}/etc/ssl/certs/ca-bundle.crt"
+    ];
+  };
+}