Create CI test matrix for supported podio versions #480
Description
There have been several instances now where Podio added or removed functionality, and the JANA2 implementation either adopted the new functionality too early, breaking builds with older Podio versions, or dropped support for the removed functionality too late, breaking builds with newer podio versions. This is easy to fix by documenting the range of Podio versions JANA2 officially supports, and setting up a test matrix in CI.