Log when an instance is killed by apprunner or exits early

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**Tell us about your request**
Log (or in some way make available) when an instance is killed because of failed health checks or because the container exited. It is extremely important information to have when debugging issues.

**Describe alternatives you've considered**
I could use Fargate because the old tasks show if the container exited or if the health checks failed.

**Additional context**
Somewhat related to https://github.com/aws/apprunner-roadmap/issues/99

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