TriggerConfigFlags: add help messages and fix unit tests

• Add a help message to all trigger flags.
• The TriggerConfigFlags unit tests were not actually running because they were invoked wrongly. Also add a unit test for loading all dynamic flags.

Click for example help output

> python -m TriggerJobOpts.TriggerRecoConfig --help Trigger
flags:
  {Calo,CostMonitoring,DecisionMakerValidation,FPGATrackSim,FSHad,HLTSeeding,ITkTracking,InDetTracking,Jet,L1,L1MuonSim,MUCTPI,Offline,Online,egamma,endOfEventProcessing}
                        Flag subcategories:
    Calo                Trigger.Calo flags
    CostMonitoring      Trigger.CostMonitoring flags
    DecisionMakerValidation
                        Trigger.DecisionMakerValidation flags
    FPGATrackSim        Trigger.FPGATrackSim flags
    FSHad               Trigger.FSHad flags
    HLTSeeding          Trigger.HLTSeeding flags
    ITkTracking         Trigger.ITkTracking flags
    InDetTracking       Trigger.InDetTracking flags
    Jet                 Trigger.Jet flags
    L1                  Trigger.L1 flags
    L1MuonSim           Trigger.L1MuonSim flags
    MUCTPI              Trigger.MUCTPI flags
    Offline             Trigger.Offline flags
    Online              Trigger.Online flags
    egamma              Trigger.egamma flags
    endOfEventProcessing
                        Trigger.endOfEventProcessing flags
  Trigger.AODEDMSet     : list of EDM objects to be written to AOD (default: None)
  Trigger.DecodeHLT     : enable decoding of HLT trigger decision/result in reconstruction (default: True)
  Trigger.EDMVersion    : Trigger EDM version (determined by input file or set to the version to be produced) (default: None)
  Trigger.ESDEDMSet     : list of EDM objects to be written to ESD (default: 'ESD')
  Trigger.ExtraEDMList  : list of extra EDM objects to be stored (for testing) (default: [])
  Trigger.ROBPrefetchingOptions
                        : select ROB prefetching types, empty list disables prefetching (default: [<ROBPrefetching.InitialRoI: 'InitialRoI'>, <ROBPrefetching.StepRoI: 'StepRoI'>, <ROBPrefetching.TauCoreLargeRoI: 'TauCoreLargeRoI'>])
  Trigger.ZdcLUT        : path to Run3 ZDC LUT (default: 'TrigT1ZDC/zdcRun3T1LUT_v2_08_08_2023.json')
  Trigger.availableRecoMetadata
                        : list of enabled trigger sub-systems in reconstruction: ['L1,'HLT'] (default: None)
  Trigger.disableCPS    : disable coherent prescale sets (for testing with small menu) (default: False)
  Trigger.doCalo        : enable calorimeters (default: True)
  Trigger.doEDMVersionConversion
                        : convert Run-1&2 EDM to Run-3 EDM (default: False)
  Trigger.doHLT         : run HLT selection algorithms (default: False)
  Trigger.doID          : enable Inner Detector (default: True)
  Trigger.doLVL1        : enable L1 simulation (default: None)
  Trigger.doMuon        : enable muon systems (default: True)
  Trigger.doNavigationSlimming
                        : enable Navigation slimming for RAWtoXYZ or AODtoDAOD transforms (default: True)
  Trigger.doOnlineNavigationCompactification
                        : enable trigger Navigation compactification into a single collection (default: True)
  Trigger.doRuntimeNaviVal
                        : Check validity of each Decision objects in the entire decision tree (CPU expensive). Also enable per-step decision printouts. (default: False)
  Trigger.doTransientByteStream
                        : create transient BS (for running on MC RDO with clients that require BS inputs) (default: None)
  Trigger.doValidationMonitoring
                        : enable additional validation histograms (default: False)
  Trigger.doZDC         : enable ZDC system (default: False)
  Trigger.enableL1CaloLegacy
                        : enable Run-2 L1Calo simulation and/or decoding (default: True)
  Trigger.enableL1CaloPhase1
                        : enable Phase-1 LVL1 calo simulation and/or decoding for Run-3+ (default: None)
  Trigger.enableL1MuonPhase1
                        : enable Run-3 LVL1 muon decoding (default: None)
  Trigger.enableL1TopoBWSimulation
                        : enable bitwise L1Topo simulation (default: False)
  Trigger.enableL1TopoDump
                        : enable L1Topo simulation to write inputs to txt file (default: False)
  Trigger.fastMenuGeneration
                        : avoid re-merging CAs that were already seen once (default: True)
  Trigger.generateMenuDiagnostics
                        : print debug output from control flow generation (default: False)
  Trigger.triggerConfig
                        : Trigger configuration source (https://twiki.cern.ch/twiki/bin/view/Atlas/TriggerConfigFlag) (default: None)
  Trigger.triggerMenuSetup
                        : name of the trigger menu (default: 'MC_pp_run3_v1_BulkMCProd_prescale')
  Trigger.writeBS       : enable bytestream writing of trigger information (default: False)

optional arguments:
  -h, --help            show this help message and exit