Add Lambda sample to GitHub Actions

[mitchell-elholm]

• Adds the Lambda sample to GitHub actions
  • Deploys the CDK with a DSQL cluster and Lambda function
  • Executes the Lambda function, checks there was no error
  • Destroys the CDK deployment, removing cluster and everything else

By submitting this pull request, I confirm that my contribution is made under
the terms of the MIT-0 license.

Thank you for your contribution!