Add standard tests for the chain GEN - SIM with gen event record in HepMC3 format

[mkirsano]

The parallel codes that use HepMC3 and the corresponding CMSSW products are being developed now, aiming at full substitution of HepMC by HepMC3 in future. For the moment they are not included in the standard tests used for PR. Such tests are to be developed.

[cmsbuild]

cms-bot internal usage

[cmsbuild]

A new Issue was created by @mkirsano.

@Dr15Jones, @antoniovilela, @makortel, @mandrenguyen, @rappoccio, @sextonkennedy, @smuzaffar can you please review it and eventually sign/assign? Thanks.

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[mkirsano]

assign generators

[cmsbuild]

New categories assigned: generators

@bbilin,@lviliani,@menglu21,@mkirsano you have been requested to review this Pull request/Issue and eventually sign? Thanks

[mkirsano]

@joonblee @shimashimarin

[mkirsano]

For my tests I use the configurations pythia8hmc3G4Jets_cfg.py and JetPlotsExample.py that can be found in /afs/cern.ch/user/m/mkirsano/public/. If they are run one after another, the file GenJetPlotsExample.root is produced with several jet histograms. They can be used for validation. The configurations mentioned will be added to GeneratorInterface/Pythia8Interface/test