Change FastSim vertex smearing to FullSim approach

First step in streamlining the FastSim configuration to FullSim
Up till know FastSim smeared the primary vertex of the gen event inside the FastSim Producer, with dedicated vertex smearing classes.
Now this is done by a VtxGenerator, as for FullSim, before the FastSim producer is called.
The PileUpProducer still uses the dedicated vertex smearing classes.
These classes will be moved to the PileUpProducer package in a next commit / pr
This allows to simplify the FastSim code, and the FastSim related python code in the ConfigBuilder.