support extensions to graphql response

[a8t3r]

https://graphql.org/learn/response/#extensions
https://smallrye.io/smallrye-graphql/1.9.3/extensions/
https://smallrye.io/smallrye-graphql/1.9.3/custom-error-extensions/

The final top-level key allowed by the GraphQL specification in a response is the extentions key. This key is reserved for GraphQL implementations to provide additional information about the response and though it must be an object if present, there are no other restrictions on what it may contain.

{
  "data": {
    "superHero": {
      "name": "Wolverine",
      "location": null
    }
  },
  "errors": [{
    "message":"location unknown",
    "path": ["superHero","location"],
    "extensions":{"code":"location-unknown"}
  }]
}

{
  "data": {
    "shirt": {
      "size": "L"
    }
  },
  "extensions": {
    "country": "Germany",
    "pi": 3.1415926535
  }
}