[ECR] [Replication]: EventBridge events that fire when an image is replicated

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**Tell us about your request**
I'd like to get EventBridge events when an image is replicated. These events should fire in the source registry (after the final destination completes) & the destination registry (for each destination).

**Which service(s) is this request for?**
ECR

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
I'd like to build workflows that trigger once the image is available in a destination region or finish a job in a source region once all regions have been replicated to.

**Are you currently working around this issue?**
N/A.

**Additional context**
This issue was filed by the ECR team. Please let us know if you have a use case for this feature / help us prioritize.

**Attachments**
If you think you might have additional information that you'd like to include via an attachment, please do - we'll take a look. (Remember to remove any personally-identifiable information.)

No repository files, tests, or entry points are identified. Start by reviewing the ECR replication request and its proposed EventBridge behavior in the issue; done would require the requested source- and destination-registry events to fire at the stated replication points.

Written by the indexing model from the issue text.