DD4hep conditions Part 1: Enable the use of conditions during the event loop

@gcorti @clemenci

This follows the discussion in Gaussino/Gaussino#15 (comment 6085263):

This means that the python configuration in Gauss has to be changed to include a few algorithms. This would give us access to conditions in the algorithms that are scheduled on top of GiGaAlg (main Geant4 simulation) that can still access the conditions via ConditionAccessor. A very good example is the work done for Muon in !901 (merged). The needed changes are:

• disable UpdateManagerSvc by setting WithoutBeginEvent=False,
• generate a fake ODIN with FakeODIN algorithm based on the run number from GenRndInit
• add the algorithm that reserves IOV: LHCb__DetDesc__ReserveDetDescForEvent for DetDesc and LHCb__Det__LbDD4hep__IOVProducer for DD4hep