title: Add mapping in AWS API Gateway to DynamoDB query with Pulumi
body: <p>I'm reading <a href="https://www.pulumi.com/docs/guides/crosswalk/aws/api-gateway/" rel="nofollow noreferrer">https://www.pulumi.com/docs/guides/crosswalk/aws/api-gateway/</a> documentation
  and its not quite clear how to use custom integrations, since AWS requires their proprietary template.
  I need to map HTTP GET request to DynamoDB query and want to do that without extra Lambda function, using mapping in API gateway. 
  Is there an example or test unit of how to achieve that in Pulumi (or using crosswalk library)?</p>