ExtendedRequestId is not present on APIGatewayProxyRequestContext

[DanielBauman88]

Is your feature request related to a problem? Please describe.
I can't access and log the ExtendedRequestId which is unique per apig request and ties my lambda request to the execution logs for my api gateway.

Describe the solution you'd like
I'd like to be able to access this variable. I can already access it for websocket requests via APIGatewayWebsocketProxyRequestContext but it is missing for other requests.

Describe alternatives you've considered
I can avoid using this library and integrations that depend on it like https://github.com/awslabs/aws-lambda-go-api-proxy and then process the lambda input myself but that defeats the point of this great package.

Additional context
I created a PR for this here #451

[DanielBauman88]

When will a release be created so that I can use this change?