feat: add go sample for API Gateway

[retgits]

As discussed with @stack72, here's a PR that adds a Go sample for an AWS Lambda function with API Gateway. This sample extends the existing aws-go-lambda sample with new functionality:

• Adding an API Gateway
• Adding an API Gateway method and resource
• Adding a trigger to the AWS Lambda function
• Adding an API Gateway Deployment

The result is a deployed API Gateway, which sends messages to the AWS Lambda function and returns the result.

$ curl https://<gateway-id>.execute-api.us-west-2.amazonaws.com/prod/helloworld   
HELLOWORLD

[stack72]

Thanks for your work here @retgits :) I made 1 change locally and then pushed the changes! This is an awesome example!