allow user to specify config values to overwrite in run_stardis function

[jvshields]

This lets the user add additional arguments to the run_stardis function to update or overwrite config values. It allows for much more flexible simulations at the python level, like running simulations in a loop with a list of different elemental rescaling values. It specifically bypasses the need to remake or change the config if you want to change some individual part of the simulation.