Track add and remove items from cart to support Power BI reporting

Description

When saving a cart, Commerce now stores changes (delta) against the previous cart. To do this, we supply an extension point in the tracking data where a partner can put the delta.
Note this data only goes to the Profile Store tracking and not to the Perform recommendation service, because the latter does not know how to handle it.
For more information, see https://world.episerver.com/documentation/developer-guides/tracking/product-tracking#sending.