Make it possible to store more version information of generated EDMs

[tmadlener]

We currently store the schema version of all datatypes that we encounter during writing, but it should also be possible to add the "package version" of an EDM to the file. E.g. EDM4hep has an edm4hepVersion.h header similar to what we have in podio, which defines a version (not entirely) independent of the schema version. There should be some hook that makes it possible to easily pick up those versions as well and add it to the metadata.