Enable legacy HLT monitoring in MT mode (ATR-22732)
Minimal changes for DQ "mixed mode" (legacy HLT + Run 3 everything else). Automatically enable this if the trigger EDM is Run 2-style but threads > 0. Changes added to avoid an ERROR in HLTTauMon, but otherwise a lot of retrieve()
calls in legacy HLT monitoring are untouched and I do not guarantee that the data dependencies will always be satisfied - left for future MRs.