Additional key fields in Discount Predicates

Added support for accessing more resources by their key field in Discount Predicate Field Identifiers. You can now use the following in discount predicates:

• ProductDiscount Predicate Field Identifiers
  • productType.key
  • categories.key
  • categoriesWithAncestors.key
  • price.channel.key
• Cart Predicate Field Identifiers
  • customer.key
  • <address-field>.key
  • shippingInfo.taxCategory.key
  • shippingInfo.shippingMethod.key
• Cart Target
  • LineItemPredicate Identifiers
    • productType.key
    • supplyChannel.key
    • price.channel.key
  • CustomLineItemPredicate
    • taxCategory.key