Update Run 4 pile-up configuration

I updated the Run 4 pile-up configuration to support all three modes that we want to look at (mu=60,140,200). Note that I already tweaked pile-up fractions. It reduces the high-pt contribution a bit, but it should not have a noticeable impact at this point (I think). We should move to the new minbias "soon" anyways.

This MR also enables ART tests including MP support which is now there!

/cc @npetters @tstreble @nstyles @pagessin @lgagnon @jchapman