Properly propagate input cellID encodings to outputs

[tmadlener]

BEGINRELEASENOTES

• Set the CellID encoding string in initialize as doing it during the event loop will no longer work (see key4hep/k4FWCore#400
• Switch to the newly available utilities for setting the cell id encoding (Add more utility functions for setting collection level parameters k4FWCore#391](Add more utility functions for setting collection level parameters k4FWCore#391))
• Propagate the cell id encoding of the input collection downstream instead of using a hardcoded collection name.

ENDRELEASENOTES

Noticed this in the downstream build of k4MarlinWrapper

[tmadlener]

I don't know how the tests can currently run because EcalBarrelCollection does not exist in the input file it is ECalBarrelCollection. e.g.

$ podio-dump -c metadata build/test/input_files/20240905_gammaFromVertex_10GeV_uniform_10events_reco_edm4hep.root | grep -i ecalbarrel
Warning in <TClass::Init>: no dictionary for class edm4hep::Vector2i is available
ECALBarrel__CellIDEncoding                    std::string  1         
ECalBarrelCollection__CellIDEncoding          std::string  1         

I have changed this to use one of the input collections instead, so we have higher chances of propagating the correct input encoding.

[jmcarcell]

I think you got confused, there is no Ecal... collection with lowercase c in the original code, but it is there in your intermediate commits. The tests never succeeded with it, but the comment above implies otherwise.

Other than that, the PR looks good.