Custom Fields for Cart Discount

We now provide custom fields on CartDiscounts. This allows users to customize their cart discounts in any way they want and fetch them by filtering on custom fields now supported on the cart discounts endpoint.

• [API] Added a custom field to the CartDiscount and CartDiscountDraft.
• [API] Added Set Custom Type and Set CustomField update actions to manage the custom fields on a cart discount.
• [API] Added support for predicates like custom(field(field_name="field_value")) on Query CartDiscounts endpoint.