Changes to List Discounts

added the required property items/items/oneOf[subschema #1: DiscountFixedOnceForeverDuration]/max_redemptions_per_customer to the response with the 200 status

added the required property items/items/oneOf[subschema #2: DiscountFixedRepeatDuration]/max_redemptions_per_customer to the response with the 200 status

added the required property items/items/oneOf[subschema #3: DiscountPercentageOnceForeverDuration]/max_redemptions_per_customer to the response with the 200 status

added the required property items/items/oneOf[subschema #4: DiscountPercentageRepeatDuration]/max_redemptions_per_customer to the response with the 200 status