Automatically update examples

[nichollsh]

It is useful to store example results for several reasons:

• when demonstrating what the model can do
• knowing what sort of thing to expect when running the model
• comparison with previous results following changes to the model
• sanity checks

There are currently two examples, which I ran manually from the 'default' and 'dummy' configs, and then copied to the examples folder with 'tools/MakeExample.sh`. However, they are now out of date.

It would be better if these examples were automatically updated. This could potentially operate via a GitHub action, triggered when a release is created.

[nichollsh]

A prerequisite for this is to have PROTEUS running via GitHub actions. This should be done through a separate issue, and is also related to implementing some more tests.