Add xe0noL1_l2fsperf_trkmht_LRT to MC_pp_v8 in 21.3 to provide a full-scan HLT LRT collection in xAOD for Run 3 trigger performance studies
WIP tag added pending comment & approval from the Trigger menu coordinators @markowen @ckaldero particularly regarding whether to add this to the MC prescale set or a dedicated LRT prescale set
This fulfills the menu request in ATR-21967