Add postInclude for adding length integrator user action to a job
The other part of moving from !41650 (closed) (along with !41741 (merged)). It's a bit less clear to me here that having this as a PostInclude is necessarily the best way to add this tool. However, it wasn't clear to me how else to do it simply such that this can be added to an arbitrary simulation job; the other UserActions seem to get configured and added based on what overall Simulation config is selected (e.g. ATLFastII, ISF, etc) which doesn't seem like what we want to do for this one.
Possibly the actual implementation of this as a PostInclude can also be improved (I struggled to get the private tools to work in a simpler manner, but that is likely just due to my own lack of familiarity with the new CA-based approach).