Add a tutorial source generator script

# ✨ Feature Request

We should add a small script for generating source data to be used in the tutorial/example app.

## Requirements

A small python script that makes use of the ants stock cube generator functions to create and save some sample data (in netCDF and possibly other formats).

## Context

This would be used as part of the tutorial on adding a new ancillary application using ANTS.

Locate the ANTS stock cube generator functions and the tutorial or example-app context first. Create and run the small Python script to generate sample source data, then verify that it saves usable netCDF output and any additional agreed formats for the ancillary-application tutorial.

Written by the indexing model from the issue text.