Add response header/body data holder to ExchangeHint

At the moment, CRISP API doesn't provide a way to read the response headers or body data if the response status code is not in 2xx range.
This is a shortcoming if a backend REST service requires a client to check response status code, header or body.

For example, commercetools defines the http errors:

• https://docs.commercetools.com/http-api-errors.html

When error occurs, the backend informs the client of the error with details like the following example:

{
  "statusCode": 400,
  "message": "First error message",
  "errors": [
   { "code":"SomeErrorCode", "message": "First error message" },
   { "code":"SomeErrorCode", "message": "Second error message" }
  ]
}

The response header may contains 400, 404, 500, etc.
And, the response body is structured like the above example: redundant status code in body and detailed message and error info, which are valuable information to client callers.

Therefore, we need a way to provide CRISP callers with ability to access those response headers and body data somehow.