Add a more descriptive error for 429 Errors/errors with no body

[nihalbhatnagar]

When we receive an error response from API Gateway, we try and parse the body of the response. For some errors(specifically a 429), there is no response body, so a call to response.json fails and logs an "Unexpected end of JSON input" error instead of passing on the response. We should ensure we don't swallow the error in this case.