xAOD::EventAuxInfo_v3, master branch (2021.11.30.)

Introduced xAOD::EventAuxInfo_v3 as a copy of xAOD::EventAuxInfo_v2, with the beam-spot variables removed. So that they could be handled as decorations from now on.

Updated the POOL converter package to introduce T/P converters implementing the schema evolution to the new _v3 type.

I was meaning to introduce a specific test in xAODEventInfoAthenaPool for the v2 -> v3 test, but couldn't find any release 22 reference AODs under /cvmfs/atlas-nightlies.cern.ch/repo/data/data-art/aod. 😕 @ssnyder, what is the procedure for putting a new one of these in place?

This is meant to be the first step in solving ATLASRECTS-6707. The algorithmic code for filling the beam-spot information shall come in follow-up MRs.

Note: In the end an algorithm (xAODMaker::EventInfoBeamSpotDecoratorAlg) was added into this MR already for filling the beamspot information correctly in data reconstruction jobs.