Added update actions to set Price tiers on Standalone Prices

You can now update Price tiers on existing Standalone Prices. Before, you had to delete and to recreate the Standalone Price with the new Price tier to achieve this.

Changes:

• [API] Added Add Price Tier, Remove Price Tier, and Set Price Tiers update actions to the Standalone Prices API.
• [API] Added Standalone Price Tier Added, Standalone Price Tier Removed, and Standalone Price Tiers Set Messages.
• [GraphQL API] Added the following types to the GraphQL schema: AddStandalonePriceTier, RemoveStandalonePriceTier, SetStandalonePriceTiers, StandalonePriceTierAdded, StandalonePriceTierRemoved, StandalonePriceTiersSet
• [GraphQL API] Changed the StandalonePriceUpdateAction type:
  • Input field removePriceTier was added to StandalonePriceUpdateAction type
  • Input field addPriceTier was added to StandalonePriceUpdateAction type
  • Input field setPriceTiers was added to StandalonePriceUpdateAction type

The following changes were introduced in terms of GraphQL SDL:

extend input StandalonePriceUpdateAction {
  addPriceTier: AddStandalonePriceTier
  removePriceTier: RemoveStandalonePriceTier
  setPriceTiers: SetStandalonePriceTiers
}

input AddStandalonePriceTier {
  tier: ProductPriceTierInput!
}

input RemoveStandalonePriceTier {
  minimumQuantity: Int!
}

input SetStandalonePriceTiers {
  tiers: [ProductPriceTierInput!]!
}

type StandalonePriceTierAdded implements MessagePayload {
  tier: ProductPriceTier!
  type: String!
}

type StandalonePriceTierRemoved implements MessagePayload {
  tier: ProductPriceTier!
  type: String!
}

type StandalonePriceTiersSet implements MessagePayload {
  tiers: [ProductPriceTier!]!
  previousTiers: [ProductPriceTier!]!
  type: String!
}