Workflows to flag used/unused executable options and config sections

[GarethCabournDavies]

So that we can ensure that the config files are an accurate record of what has been run, and not be confusing, we should add a check into the workflow geneation to monitor a couple of things:

• Unused config sections
• Unused options in the executables section

This will help avoid issues like the one seen by Yifan (reported in slack) where executables from dependencies are removed, so the ${which|...} will fail, but it is not actually used, and so we can remove it from the configs anyway.