Add better aggregate controls

[kirangadhave]

We have a single Aggregate button which aggregates with the mean operation. It would be useful to have multiple controls for options like: Aggregate Sum, Aggregate Mean, Aggregate Group-By.

Aggregate Group-by creates the group-by object without any operation specified. In terms of visualization, we can show this by a convex hull (maybe?) instead of adding the aggregate point and removing the original points.

[kirangadhave]

@alexsb I don't recall what the Aggregate Group-by does. Was it to allow selecting any aggregation operation?

[alexsb]

It creates a group-by object instead of a dataframe, where the aggregate function can later be specified in code.

[kirangadhave]

ah that makes sense.

[kirangadhave]

To check:

• add warning when aggregating with sum operation, if the field is not aggregate encoding