Add more combination examples

[seb86]

For example adding a variation with custom item data.

var data = {
  "id": "1820",
  "quantity": "1",
  "variation": {
    "attribute_colours": "Red",
    "attribute_pa_size": "2x-large"
  },
  "item_data": {
    "engraved_name": "Sébastien Dumont",
    "engraved_size": "Medium"
  }
};

CoCart.post("cart/add-item", data)
.then((response) => {
  // Successful request
  console.log("Response Status:", response.status);
  console.log("Response Headers:", response.headers);
  console.log("Response Data:", response.data);
})
.catch((error) => {
  // Invalid request, for 4xx and 5xx statuses
  console.log("Response Status:", error.response.status);
  console.log("Response Headers:", error.response.headers);
  console.log("Response Data:", error.response.data);
})
.finally(() => {
  // Always executed.
});