nl-core-preferred-pharmacy as core extension

[ahenket]

I have created FHIR-38703 to open up the possibility that our Dutch extension nl-core-preferred-pharmacy could be promoted as international core extension.

[ahenket]

The extension was approved and created, although still in build.fhir.org. See:

https://build.fhir.org/ig/HL7/fhir-extensions/StructureDefinition-patient-preferredPharmacy.html