Ensure that Amazon ECR image repositories are using lifecycle policies.

Amazon ECR lifecycle policies provide more control over the lifecycle management of images in a private repository. A lifecycle policy contains one or more rules, where each rule defines an action for Amazon ECR. This provides a way to automate the cleaning up of your container images by expiring images based on age or count. You should expect that after creating a lifecycle policy, the affected images are expired within 24 hours. When Amazon ECR performs an action based on a lifecycle policy, this is captured as an event in AWS CloudTrail.