classifierext: add HEP ontology

* Adds the DESY maintained HEP ontology to classifier.

Co-authored-by: Kirsten Sachs <kirsten.sachs@desy.de>
Co-authored-by: Florian Schwennsen <florian.schwennsen@desy.de>
Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>