TrigGlobalEfficiencyCorrection adjustments for 2023 triggers and missing scale factors

Changes in the TrigGlobalEfficiencyCorrection for 2023 triggers:

• add electron trigger definitions for 2023 (based on https://twiki.cern.ch/twiki/bin/view/Atlas/TrigEgammaRecommendationsRun3);
• but there are no scale factors provided so far, so just fixing the above wouldn't prevent failures either in initialisation (when using the suggest***MapKeys() functions, as reported by @dbaronmo), or during runtime.

Since it might be more generally useful, this MR introduces a special keyword RETURN_DEFAULT_SCALE_FACTOR to be used as a special entry of the ListOfLegsPerTool map property to explicitly list all trigger legs for which no tool can be provided. The idea is that if one event requires input efficiency for such a leg, the tool will then return a global SF of 1 without errors / warnings, instead of failing.

A dedicated test case was added in the TrigGlobEffCorrValidation test script.

EDIT after discussion (see thread below) took this out: Also added some rows in MapKeys.cfg for 2023 electron triggers to make use of this new feature.

Finally, corresponding adjustments were made in TrigGlobalEfficiencyCorrectionAlg (👋 @ravinab, does this whole thing seem reasonable to you?) to not create electron/photon tools for that particular keyword, although I haven't tested.