refactor: massive refactor in spec generator primarily

more modular code, preparing for harvesting / generalisation (for other ontologies)
different dprod.jsonld: is now simply a rdflib.serialize version of the DPROD OWL file
new dprod-shapes.jsonld file, serialization of the dprod-shapes.ttl file
dprod-dcatprofile.ttl renamed to dprod-shapes.ttl for consistency reasons
generating *.-all.rdf/ttl/jsonld files that combine all triples from the dprod:, dprod-shapes: and dcat: ontologies
moved all references in the spec to the respec-compliant appendix
build.sh script more advanced, enforces you to use Python 3.12 as a minimum
Makefile simply calls build.sh

EKGF / dprod