How to work around missing CDK features (overrides)

[Doug-AWS]

Replaces this issue created by ccfife on Apr 15 in the CDK repo: aws/aws-cdk#2294.

Original description:

This is a new topic for the how to section, and is largely covered "Accessing the AWS CloudFormation Layer" topic in the current guide. We just need to review the topic and make sure it is at the quality bar we want. We've learned that customers need to use the "escape hatch" to address specific use cases the L2 don't address yet.

[Doug-AWS]

https://docs.aws.amazon.com/cdk/latest/guide/cfn_layer.html