Added CA configs for alternative MergeMcEvent modes. Also removes ExpectLowPtMinBiasBackgroundCollection and ExpectHighPtMinBiasBackgroundCollection for legacy config, as the arguments do not appear to exist any more.
Relevant for ATLSWUPGR-167
Unfortunately the NewMerge config does not run
StandardInTimeO... ERROR WriteHandle already valid??
StandardInTimeO... ERROR PileUpComps/src/PileUpToolsAlg.cxx:89 (StatusCode PileUpToolsAlg::execute()): code FAILURE: puToolHandle->prepareEvent(Gaudi::Hive::currentContext(), eventsToProcessByTool[&(*puToolHandle)])but merging the config regardless to have it available for debugging.
FYI @jchapman