Minimum requirement is now optional on automatic discounts

Previously merchants were required to specify minimum purchase conditions on product, order, and free shipping automatic discounts. We're now making these conditions optional, so the minimumRequirement field in our APIs is now able to return a null value.

As of version 2025-01, the minimumRequirement field for both DiscountAutomaticBasic and DiscountAutomaticFreeShipping will become nullable.