Management APIs should provide detailed responses to errors (ban EnsureStatusCode)

Currently, the Management APIs make extensive use of HttpResponse.EnsureStatusCode() internally. This raises an HttpRequestException with a Message that mentions the failing status code, but no other details.

This leaves our end users with nothing to go on when investigating while their management calls failed, unless they use WireShark or Fiddler to capture the HTTP traffic.

At the very least, if the response from the server is JSON, we should propagate that body back up to the end user in the exception.

The RFC does not specify for or against this behavior.
https://github.com/couchbaselabs/sdk-rfcs/blob/master/rfc/0054-sdk3-management-apis.md