Show correct quantity when order Adobe offers and under subscriptions

As a vendor, I want to indicate one of the number boxes in a pricing plan as the "quantity" for the entire plan, so that it's possible to show to customers on UI, in reports etc.

Includes:

1. Instructions for vendor to use "quantityKey" as Number field key - Team 2, CPQ

2. Displaying the value of Number field with "quantityKey" as Quantity - Team 1

3. Updating Number field key of all existing pricing plans and subscriptions, with migration - Team 2, AI