Add tutorial for modifying schema input options

[lilyminium]

Is your feature request related to a problem? Please describe.

I'm uncertain how public facing this kind of thing actually should be, but this has come up a couple times and is not really documented anywhere. I've just written up an example that integrates well with the existing Tutorial 4 -- we should consider including it. https://github.com/openforcefield/discussions/issues/51

FYI, due to the different structure of the protocols the equilibration part of that code will not work for workflows like the EquilibrationLayer and PreequiilibratedSimulationLayer as the equilibration protocol is also a part of a conditional group there.