set node property `highest_FDA_approval_status` in DrugBank XML ingest

[saramsey]

FUTURE ENHANCEMENT:

For KG2.10.4 (or whatever we are calling the next KG2 build after KG2.10.3), we decided that we would try to update the DrugBank ingest script (convert_drugbank_xml_to_kg_jsonl.py) to set a node property highest_FDA_approval_status for FDA-approved drugs (which will have category biolink:ChemicalEntity). This will take some work to ensure that this new property flows smoothly through the build process, the graph merge, normalization, etc. But if successful, then FDA approval information will be available as a node property, and in the Biolink-approved slot for representing FDA drug approval status. This, in turn, will make it trivially easy to generate the fda_approved_drugs_v1.0_KG2.XX.Xc.pickle file without having to re-ingest the DrugBank XML file.