kedro-airflow: Grouping in memory is not working properly

[ankatiyar]

Description

The --group-in-memory flag is a new addition #241 and hasn't been released yet.

Running kedro airflow create --group-in-memory and kedro airflow create with the spaceflights project creates the exact same DAGs - there's some issue in the determining whether a dataset is MemoryDataset

kedro-plugins/kedro-airflow/kedro_airflow/grouping.py

Lines 14 to 15 in fbe545f

	dataset = catalog._datasets.get(dataset_name, None)
	return dataset is not None and isinstance(dataset, MemoryDataset)

^ returns None for datasets that are not in the catalog (dataset factory datasets or MemoryDatasets

There might also be some problems with dataset factories - still investigating

[astrojuanlu]

cc @sbrugman FYI!