Particle gun simulation

Production of particle gun simulation (of some signal decay) in Run3 seems not be fully supported at the moment. The Gauss and Boole steps can be run as in Run2, but for Moore there don't seem to be dedicated pGun options. The problem that has to be addressed is how the PV simulated in Gauss by PGPrimaryVertex that is then propagated through Boole, can be read in/used by Moore.

In Run2, one could directly go to Brunel after Boole, and the Moore step could be skipped. In Brunel it seems like the only thing that was done differently for pGun simulation is to remove the vertexing from the reconstruction sequence, see here.

In Run3 the reconstruction happens already in Moore, so something similar would have to be implemented.