feature request: provide the response body with UnexpectedStatusCode error

[justenwalker]

Description

When the API returns a response that isn't one of the expected response codes, the generated code returns

return res, validate.UnexpectedStatusCode(resp.StatusCode)

However, this is nearly useless because it only contains the status code. There is no way to look at the body of the request to debug without editing the generated code and seeing what response was given.