Pivot Table - Ability to add row and column percentage statistics

**What's your use case?**
If I am using the Pivot table widget to create a "crosstab", it would be nice if I could use use the Count aggregation but also define row and column percentages. We can already add additional aggregations, so this would simply extend that idea to also show the % of totals via row and column.

**What's your proposed solution?**
Add options for count tables to show the distributions.


**Are there any alternative solutions?**

A crosstab widget where counts are the core aggregation against two categorical entries.

Start by locating the Pivot table widget and its existing additional aggregation options. Determine how count tables could expose row and column percentage distributions; the feature is done when both percentage views can be added alongside counts and their displayed totals match the crosstab data.

Written by the indexing model from the issue text.