FPGATrackSim fix truth and allow for small wrapper metadata
These small changes are to fix one bug and to add one small feature to FPGATrackSim. The bug (https://its.cern.ch/jira/browse/EFTRACK-382) is that the shared_ptr for our truth objects was going out of scope and so we didn't ever anymore save truth info for hits. Passing by reference fixes this. The feature is allowing users to pass a small string of meta data to store in the wrapper files. This is optional. Tagging @tbold for his opinion before removing the Draft on this...