TrigP1Test: migrate decodeBS step to CA

Migrate the "DecodeBS" step of our ART testing framework to CA and move the script to the TrigP1Test package as it should not be used outside of validation.

Trigger/TrigValidation/TrigP1Test/python/DecodeBS.py

+# Copyright (C) 2002-2023 CERN for the benefit of the ATLAS collaboration
+#
+# Script to unpack (Run-3) HLT bytestream and write ESD file. Only to be used
+# for validation purposes. For reconstruction use the full TriggerRecoConfig.
+#
+
+from AthenaConfiguration.MainServicesConfig import MainServicesCfg
+from AthenaConfiguration.AllConfigFlags import initConfigFlags
+from TriggerJobOpts.TriggerByteStreamConfig import ByteStreamReadCfg
+from TriggerJobOpts.TriggerRecoConfig import Run3TriggerBSUnpackingCfg, TriggerEDMCfg
+
+# Set and parse flags
+flags = initConfigFlags()
+flags.parser().add_argument('--moduleID', type=int, default=0, help='HLT module ID to decode')
+args = flags.fillFromArgs()
+
+flags.Output.ESDFileName = 'ESD.pool.root' if args.moduleID==0 else f'ESD.Module{args.moduleID}.pool.root'
+flags.lock()
+
+cfg = MainServicesCfg(flags)
+cfg.merge( ByteStreamReadCfg(flags) )
+
+acc_bs = Run3TriggerBSUnpackingCfg(flags)
+acc_bs.getEventAlgo('TrigDeserialiser').ModuleID = args.moduleID
+cfg.merge(acc_bs)
+
+cfg.merge( TriggerEDMCfg(flags) )
+
+import sys
+sys.exit(cfg.run().isFailure())