octavePackages: add automatic updating script based on Python's

This script is heavily based on the script used to update all python
libraries at
pkgs/development/interpreters/python/update-python-libraries/update-python-libraries.py

The Octave Packages' website uses YAML as their basis, so we must
reformat to use YAML instead of JSON.

maintainers/scripts/update-octave-shell.nix

@@ -0,0 +1,12 @@
+{ nixpkgs ? import ../.. { }
+}:
+with nixpkgs;
+let
+  pyEnv = python3.withPackages(ps: with ps; [ packaging requests toolz pyyaml ]);
+in
+mkShell {
+  packages = [
+    pyEnv
+    nix-prefetch-scripts
+  ];
+}