Importer: Update nodes already in DB

[joeflack4]

Description

From importer.py:

    def import_node_attribute(self, node_attribute):
        entity = node_attribute['entity']
        attribute = node_attribute['attribute']
        system = node_attribute['system']
        logger.info(f'Importing NodeAttribute {system}.{entity}.{attribute} ...')

        na_node = self.mdr_graph.get_node_attribute(system, entity, attribute)
        if na_node is not None:  # already exists. Skip
            # TODO: Update the node
            return

    def import_harmonized_attribute(self, harmonized_attribute):
        system = harmonized_attribute['system']
        entity = harmonized_attribute['entity']
        attribute = harmonized_attribute['attribute']
        logger.info(f'Importing HarmonizedAttribute {system}.{entity}.{attribute} ...')

        ha_node = self.mdr_graph.get_harmonized_attribute(system, entity, attribute)

        if ha_node is not None:  # already exists. Skip
            # TODO: Update
            return