Fetch attribute values and labels for customAttributeMetadata

[cjelger]

It would be really useful to be able to get all the possible values and labels for "select" attributes. For example with the following request there is currently no way to get all the values and labels for the "color" attribute.

{
  customAttributeMetadata(
    attributes: {
      attribute_code: "color"
      entity_type: "4"
    }
  ) {
    items {
      attribute_code
      entity_type
      attribute_type
    }
  }
}

Acceptance criteria

1. The service response should be restructured and extended as follows:

[{
    "__implements": "EavAttributeInterface",
    "__typename": "DropdownEavAttribute",
    "entity_type": "catalog_product",
    "render_metadata": {
        "__typename": "EavAttributeRenderMetadata",
        "input_type": "dropdown",
        "value_type": "Int"
    },
    "attribute_code": "color",
    "options": [
        {
            "__typename": "EavAttributeDropDownOptionMetadata",
            "label": "Red",
            "value": 4 // Derived from "value_type" above (just an example of the utility)"
        },
        {
            "label": "Blue",
            "value": 5
        }
    ]
}]

2. Changes should be covered with web API functional tests. See \Magento\GraphQl\Catalog\ProductViewTest::testQueryAllFieldsSimpleProduct as an example.

Alternative options that were considered:
It would be great to have the possibility to extend the response with something like:

{
  "data": {
    "customAttributeMetadata": {
      "items": [
        {
          "attribute_code": "color",
          "entity_type": "4",
          "attribute_type": "Int"
          "options": [
            {
              "value": "1",
              "label": "Green"
            },
            {
              "value": "2",
              "label": "Red"
            }
          ]
        }
      ]
    }
  }
}

Another alternative could be to be able to get the label for the attributes of ProductInterface. For example, color currently returns an Int, but it would be great to also be able to get the label for the value, so something like:

color {
  value
  label
}

[klimart]

Sample query:

{
  customAttributeMetadata(
    attributes: {
      attribute_code: "color"
      entity_type: "4"
    }
  ) {
    items {
      attribute_code
      entity_type
      attribute_type
      attribute_options {
        value
        label
      }
    }
  }
}

[klimart]

Github Pull Request:
#108

[naydav]

#108