acdh-oeaw/rdf-fastapi-utils: callback function

adds the possibility to add a callback function that gets the value of a field and should return a value

citation: str = Field(..., rdfconfig=FieldConfigurationRDF(path="person", callback_function=get_source_mapping))

ef get_source_mapping(source):
    for key, value in source_mapping.items():
        if key in source:
            return value
    return None