Create aggregated tables with the new Direct Query to Power BI dataset feature

Recently the feature to be able to connect and "extend" Power BI datasets with your own data was released.

This is a great feature but one piece that would really enable our use of this is to be able to create aggregated tables (using the Power Bi Aggregations functionality) off of the tables in the original dataset.

A great use case for us would be to:
- Build a model with our required directquery fact tables, dual dimension tables
- Extend that model with the new "Direct Query to Power BI dataset" feature to add imported aggregated tables in the new datasets

That way we can centrally manage one "large model" from an enterprise perspective, and have developers and self-serve users build their required imported tables off of it without impacting existing datasets