Added update action for setting external discounts on Standalone Prices

You can now set the discounted value of a Standalone Price via update action also. Before, it was only possible to set that value during creation of the Standalone Price.

Changes:

• [API] Added SetStandalonePriceDiscountedPrice update action to Standalone Prices.
• [API] Added StandalonePriceExternalDiscountSet Message.
• [GraphQL API] Added the following types to the GraphQL schema: SetStandalonePriceDiscountedPrice, StandalonePriceExternalDiscountSet.
• [GraphQL API] Changed the StandalonePriceUpdateAction type:
  • Input field setDiscountedPrice was added to StandalonePriceUpdateAction type

The following changes were introduced in terms of GraphQL SDL:

extend input StandalonePriceUpdateAction {
  setDiscountedPrice: SetStandalonePriceDiscountedPrice
}

input SetStandalonePriceDiscountedPrice {
  discounted: DiscountedProductPriceValueInput
}

type StandalonePriceExternalDiscountSet implements MessagePayload {
  discounted: DiscountedProductPriceValue
  type: String!
}