Add events for CDK custom resource provider framework.

[mawallace]

Description of changes:

There is a CDK custom resource provider framework which makes writing custom resource lambdas easier.

This adds the request/response types for lambdas used in this framework.

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• [x] I confirm that my contribution is made under the terms of the Apache 2.0 license.
• [x] I confirm that I've made a best effort attempt to update all relevant documentation.