[ATR-21373] Deprecate writing of R2 xAOD::TriggerMenu format in POOL files produced in master

Simplify the xAODMenuWriterMT.cxx such that it ONLY needs to write the Run3 metadata format. No format-shifting is needed here, unlike for the Run2 metadata format. The algorithm is greatly simplified.

Schedule the creation of the Run3 format for all Run3 data and MC (ConfigFlags.Trigger.EDMVersion == 3) and for Run2 data and MC if a secondary flag is set (ConfigFlags.Trigger.EDMVersion == 3 and ConfigFlags.Trigger.doEDMVersionConversion`)

If we read Run2 data and doEDMVersionConversion is false then we schedule the old xAODMenuWriter.

Updates the metadata reader too to support reading TriggerMenuJson_HLT and TriggerMenuJson_L1 - this is important now that there is no TriggerMenu fall-back option.