Group by dependencies for agg columns

[oelarnes]

Agg columns may depend on group_by columns, for example, you probably want gp_wr_mean to group by expansion by default.

At the moment, 'expansion' will go into the view columns structure according to manifest, but will not be grouped by and therefore passed as part of the agg_df unless it is also specified as a grouping. Probably it should just grouped by and just not selected in the final selection.