VBF region definition in bbll analysis

In the bbll analysis, we started comparing the cutflows for mc20 PHYSLITE against the legacy Run2 analysis samples. You may see Fatima's latest update here (slides 13-16): https://indico.cern.ch/event/1387008/contributions/5830324/attachments/2807867/4899902/bbll_Update_26022024.pdf

The biggest differences are spotted in the VBF veto region (the last bin of the cutflow efficiency plot), which was recently updated by Fatima in this MR: !424 (merged)

During our analysis meeting, it was pointed out (as also Fatima did in the MR) that the legacy Run2 analysis was not using the absolute value of the delta_eta distribution to determine the max delta_eta: https://gitlab.cern.ch/easyjet/easyjet/-/blob/main/bbllAnalysis/src/SelectionFlagsbbllAlg.cxx?ref_type=heads#L288

so this might be one source of discrepancy in that bin.

This is how the max_delta_eta calculation was handled in the Run2 analysis: https://gitlab.cern.ch/atlas-physics/HDBS/DiHiggs/bbll/CAFbbll/-/blob/master/Root/CombinedQuantities.cxx#L532

While the investigation of the differences in the other bins (will shortly start to implement the lepton trigger matching for a more "apples to apples comparison" with the legacy Run2) continues, we would like to discuss the VBF veto implementation here and then open a MR to change it if needed.

Tagging: @falves, @fbendebb, @aelmouss and @wollrath from the analysis team