Feat(api): add attachments

[icazevedo]

What's the purpose of this pull request?

This PR adds support for attachments on FastStore API. Attachments are a way to customize a product. If a product is added to the cart with a different attachment, a new offer should be created for it. An offer should be considered the same as another one if and only if the attachments (and its value) are also equal.

How it works?

The attachments are included under the additionalProperty field, where they can be filtered through valueReference comparison. They are received in the same format they're sent.

How to test it?

JSON variables of the graphql query to the validateCart mutation:

{
  "cart": {
    "order": {
      "orderNumber": "911b0ceef77e4b98b9ca250a5d2fab2b",
      "acceptedOffer": [
        {
          "price": 602.78,
          "listPrice": 834.97,
          "seller": {
            "identifier": "1"
          },
          "quantity": 1,
          "itemOffered": {
            "sku": "2000586",
            "image": [
              {
                "url": "http://storeframework.vtexassets.com/arquivos/ids/177382/assumenda.jpg?v=637753139967300000",
                "alternateName": "hic"
              }
            ],
            "name": "Bells add-ons",
            "additionalProperty": [
              {
                "name": "1-3-lines",
                "value": "{\"Line 1\":\"1\",\"Line 2\":\"2\",\"Line 3\":\"3\"}",
                "valueReference": "ATTACHMENT"
              }
            ]
          }
        }
      ]
    }
  }
}

Starters Deploy Preview

https://github.com/vtex-sites/nextjs.store/pull/47
vtex-sites/gatsby.store#53

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Name	Status	Preview	Updated
faststore	✅ Ready (Inspect)	Visit Preview	May 18, 2022 at 10:51PM (UTC)

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Latest deployment of this branch, based on commit 4134943:

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[igorbrasileiro]

I didn't get it, does the ouptut will be always a string, either a string or a stringified object?

[icazevedo]

It is always a string, but it can be a regular string eg. "hello world" or and stringified object "{"key": "value"}"

[igorbrasileiro]

@icazevedo great job, I left some comments that may affect this PR.