Add support for CloudFormation custom resource request/response

As described in:
* https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/crpg-ref-requests.html
* https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/crpg-ref-responses.html