Add a way to get response headers after getting a response from an API call. We need to be able to get information from headers like Idempotent-Replayed after returning a response in the SDK.

Additionally, it may be a good idea to make all "response data" including the raw response body available to developers who use the SDK. Currently only the resource is returned in a response (or an error is thrown). It could be a good idea to allow developers to introspect the actual response object for additional info (such as headers, response body and other details that the requests library may include after running an http request).