Alarm for out-of-band changes to resources within a stack

### Resource Name

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### Details

Scope of request: Since CloudFormation does not support drift detection on all resource types, it would be great to have an alarm to notify users if an out-of-band change was made on a resource that is used within a CloudFormation stack.

Expected behavior: When an out-of-band change occurs to a given resource, an alarm will be triggered and CloudFormation will notify cx that a change has been made to the stack (maybe including details of which IAM user made the change and the resource).

I'm not sure how feasible this is, but it would be very helpful since not all resources are supported for drift detection. :)

The issue names no repository files, tests, or entry points. Start by reviewing CloudFormation drift-detection coverage and the available mechanisms for observing out-of-band resource changes. Done would require an agreed design for triggering an alarm and notifying customers with the relevant stack, resource, and actor details.

Written by the indexing model from the issue text.