Geometry dumper name when converting DIGI to MDF files

I was converting some digi samples to mdf converter in Moore and noticed it creates the usual geometry folder with VP_geometry.bin instead of velo_geometry.bin. The cause is this bit of code: https://gitlab.cern.ch/lhcb/Allen/-/blob/master/Dumpers/BinaryDumpers/src/DumpVPGeometry.cpp#L97

As Allen has always used velo_geometry.bin (see https://gitlab.cern.ch/lhcb/Allen/-/tree/master/input/detector_configuration), I would change that line of code such that we can still run on the old samples geometry.

@cagapopo @dovombru