Add (unprescaled) L1_FirstBunchInTrain bit in central NANOAOD

[lathomas]

Hello,
Having in NANOAOD the (unprescaled) L1 bit decision corresponding to whether an event is in the first colliding bunch of a train (L1_FirstBunchInTrain) would be very useful for prefiring studies.
Currently only the decision after prescale is saved (which is useless).
It would be great if someone could volunteer to do that.
Thanks !
Laurent

[lathomas]

Update:
The right boolean we want is the post prescale decision of L1_FirstBunchBeforeTrain in bx-1.
Here's how to access that info:
https://github.com/iihe-cms-sw/GenericTreeProducerMINIAOD/blob/main/Ntuplizer/plugins/Ntuplizer.cc#L1057
The bit index can be found using
https://github.com/iihe-cms-sw/GenericTreeProducerMINIAOD/blob/main/Ntuplizer/plugins/Ntuplizer.cc#L1018C13-L1018C13