Add debug output for GeoModelXml copy number levels

As discussed in #37, the CNL_N are one of the more complicated things to get right when developing geometries in GeoModelXml. This MR intends to add some optional debug output which should give useful information when trying to work out the mapping of copy number levels to structures.

Suggestions for improvements (especially for how to pass optional parameters to GeoModelXml through the plugin) are very welcome.

FYI @ncalace

mentioned in commit 737b9324

merged

@dellacqu mentioned that this causes problems for the Muon plugin (not tested as part of the CI?) so maybe this should be reverted for the moment?

Hi @nstyles , it seems that @dellacqu could easily fix the plugin, as you can see here: https://gitlab.cern.ch/atlas/geomodelatlas/GeoModelATLAS/-/commit/4561f79406913fd55747ac47a6f2f0d6d4f01bd9

The pipeline of GeoModelATLAS is again green, so everything works fine!

Thanks and cheers, Marilena

Thanks @mbandier - and sorry again for the inconvenience. I'll communicate and discuss any changes which might have downstream impacts in future!