CI Testing and Documentation

[tomeichlersmith]

With fire opening up a whole new world, I am planning to copy my testing and docs-generating GitHub workflows into this repo so that g4fire can have continuous testing and documentation posting.

The biggest snag in this direction is how long it takes to build Geant4. Perhaps a container is the best approach? But I could also look at caching the dependencies like other GitHub actions.

[omar-moreno]

A container makes the most sense to avoid any Geant4 compilation madness.