[Checkout coverage] Added discount information to shopping cart

[rogyar]

Description (*)

This PR adds additional information about discount to the shopping cart details. The information contains discount amount and a label of the applied rule(s).

Fixed Issues (if relevant)

1. Add discount information to Cart #683 : Add discount information to cart

Manual testing scenarios (*)

1. Create a shopping cart price rule
2. Add product to the shopping cart and use cart response for getting he information

mutation {
  addSimpleProductsToCart(input: {
    cart_id:"X9KeOSMZuU10yww2S1A4DXfEwFpg0Q9X"
    cart_items: [
      {
        data: {
          quantity:1
          sku:"simle"
        }
      }
    ]
  })
  {
    cart {
      prices {
        discount {
          amount {
            value
            currency
          }
          label
        }
      }
    }
  }
}

or use cart query for an existing cart with a product and discount:

{
  cart (cart_id:"X9KeOSMZuU10yww2S1A4DXfEwFpg0Q9X") {
    prices {
      discount {
        label
        amount {
          value
          currency
        }
      }
    }
  }
}

[magento-engcom-team]

Hi @lenaorobei, thank you for the review.
ENGCOM-5181 has been created to process this Pull Request

[lenaorobei]

@rogyar as per latest GraphQL sync upplease consider changing label representation from comma-separated values to the array of values. Thank you.

Requirements changed

[magento-engcom-team]

Hi @naydav, thank you for the review.
ENGCOM-5181 has been created to process this Pull Request

[magento-engcom-team]

Hi @naydav, thank you for the review.
ENGCOM-5181 has been created to process this Pull Request

[ghost]

Hi @rogyar, thank you for your contribution!
Please, complete Contribution Survey, it will take less than a minute.
Your feedback will help us to improve contribution process.