Changes to Retrieve all Product Variants.

the response property items/variant/compare_at_price became nullable for the status 200

the response property items/variant/cost_per_item became nullable for the status 200

the response property items/variant/options/items/custom became nullable for the status 200

added the new optional query request parameter fields

added the optional property items/variant/discount to the response with the 200 status

added the optional property items/variant/options/items/product_option_id to the response with the 200 status

added the optional property items/variant/options/items/product_option_value_id to the response with the 200 status

added the optional property items/variant/position to the response with the 200 status

added the optional property items/variant/weight to the response with the 200 status

added the optional property items/variant/created_at to the response with the 200 status

added the optional property items/variant/updated_at to the response with the 200 status