Draft: Set verbosity of G4 event to silent as default
This should be set as default so that we can build the debug version of Gauss with VERBOSE on by default have it 'off' and allow to switch it on at run time.
This should replace Geant4!104 (merged) that would disable G4VERBOSE at build time.
Once tested an equivalent MR should be made for Gaussino
cc: @mimazure, @witoldp, @mexu, @bcouturi, @clemenci, @veltri