Function URL support: invocation_response::failure always returns "Internal Server Error"

[instw]

I'm using the C++ framework to create a lambda that's using a Lambda Function URL.
When there is an error (i.e. invocation_response::failure) , the HTTP response is always a "Internal Server Error".
This seems to be because the response needs to be in a format as detailed in https://docs.aws.amazon.com/lambda/latest/dg/urls-invocation.html - which includes the "statusCode" etc.

Ideally, invocation_response::failure should at least set the "body" in the application/json response.

As a workaround, crafting the appropriate error payload using invocation_response::success works.

[marcomagdy]

Also invocation_response has a public constructor which you can pass it a payload and whether a success or a failure response.