graphQl-864: Prevent to return a shipping address until it is set on a cart

[VitaliyBoyko]

Description (*)

Return an empty array of shipping addresses for the created empty cart until a shipping address
is set.

Fixed Issues (if relevant)

1. The shipping address contains null values when there's no shipping address set on a cart #864: The shipping address contains null values when there's no shipping address set on a cart

[magento-engcom-team]

Hi @lenaorobei, thank you for the review.
ENGCOM-5770 has been created to process this Pull Request
✳️ @lenaorobei, could you please add one of the following labels to the Pull Request?

Label	Description
Auto-Tests: Covered	All changes in Pull Request is covered by auto-tests
Auto-Tests: Not Covered	Changes in Pull Request requires coverage by auto-tests
Auto-Tests: Not Required	Changes in Pull Request does not require coverage by auto-tests

[cpartica]

The problem is that the quote api creates empty addresses placeholders before we even set them and has nothing to do with getShippingAssignments. You can set addresses independently before choosing a shipping method.

This fix is not sufficient as it breaks further if you set a shipping address but not select a shipping method, we're not returning anything and we should..
example:
let's say we set a setShippingAddressesOnCart
then we query:

query {
  cart(cart_id: "eVt0JvTe7qAm6arhkHZYEQjvcFRoiZ8C") {
   shipping_addresses {
      lastname
      firstname
      available_shipping_methods {
      carrier_code
    	}
      selected_shipping_method {
        carrier_code
        carrier_title
        method_code
        method_title
      }
    }
  }
}

Expected response:

{
  "data": {
    "cart": {
      "shipping_addresses": [
        {
          "lastname": "test lastname",
          "firstname": "test firstname",
          "available_shipping_methods": [
            {
              "carrier_code": "flatrate"
            }
          ],
          "selected_shipping_method": null
        }
      ]
    }
  }
}

Actual

{
  "data": {
    "cart": {
      "shipping_addresses": []
    }
  }
}