Add support for "products" variable to DTM

[#1]

DTM has support for eCommerce events such as prodView, but it has no native UI for setting the products variable! Right now, the official documentation suggests using custom code to set it. 

This is the worst variable in all of the collector code to work with. The syntax makes our engineers downright angry. On top of that, the recommended way of piping Satellite variables in means that you may need to make 6+ calls to _satellite.getVar() to construct it.

Having a sensible UI to set the specific parts of the product variable would be a very obvious use of DTM to set Adobe variables on demand. Please consider adding it!

[#2]

Problem is that the products variable is super specific and so many customizations (events and eVars).  Best case is to use the custom code.  If you're using a data layer, you should be able to loop through the objects and build the products variable accordingly.  This takes the weight off of the developers and allows someone with much more experience to put it all together inside of DTM.