Introduce Geantinos in the Athena

Andrii Verbytskyi requested to merge averbyts/athena:geantinos into 23.0

Add Geantino PDG codes 998/999 to the AtlasPID.h

Both geantinos are strongly interacting. One is neutral and one is positively charged.

Note: MCUtils contain a bug that considers both geantinos to be uncharged mesons, therefore one has to take that into account and adjust the reference files.

Tag @jchapman @pclark @abuckley @ewelina

Fixes ATLASSIM-6612

Edited by John Derek Chapman

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