Generate a golden output from single time step

[dorchard]

This task breaks down into a few bits

• Input configuration for a 20-year warmup, using AD99 classic
• Generate "golden" output data that can be saved and uploaded
• Automated system for then being able to re-run and check against golden output again
• ICCS team to test it

[dorchard]

We are considering using ncdiff instead of Python (so as not to add an extra dependency).