abstract CLI image generation

and add busybox in all the images

lib/buildCLIImage.nix

@@ -0,0 +1,27 @@
+{ dockerTools
+, busybox
+, cacert
+}:
+{ drv # derivation to build the image for
+# Name of the binary to run by default
+, binName ? (builtins.parseDrvName drv.name).name
+}:
+dockerTools.buildLayeredImage {
+  name = drv.name;
+
+  contents = [
+    # add a /bin/sh on all images
+    busybox
+    # most program need TLS certs
+    cacert
+    drv
+  ];
+
+  config = {
+    Cmd = [ "/bin/${binName}" ];
+    Env = [
+      "PATH=/bin"
+      "SSL_CERT_FILE=${cacert}/etc/ssl/certs/ca-bundle.crt"
+    ];
+  };
+}