Example of parallel processing of a SystemSet

I'm working on using Bevy to facilitate an ecological (scientific) simulation model. To that end, I need to repeat/replicate the positted scenario a number of times, while using already available resources, and also having some things that pertain to the
particular iteration. Also, I need to reset some resources/etc. after each run.

There is a discussion on this here #1678, where @alice-i-cecile called this

> easy parallel process replication

and also there is this RFC for SubWorlds bevyengine/rfcs#16 that could help with this.

If someone could pinpoint some way to accomplish today, that would be great so as to be able to get going for now.