Create pile-up events hash and store it in xAOD::EventInfo (ATLASSIM-3795)
It might be useful to have an information how many pile-up events repeat in an analysis (e.g. we get exactly the same mixture of minbias events). This MR adds a 128-bit MD5 hash of pile-up info to the xAOD::EventInfo objects.
Migrated from https://gitlab.cern.ch/atlas/athenaprivate1/merge_requests/14958