Support for multi-region automatic deployment from ECR

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**Tell us about your request**

Automatic deployment from ECR only works if the ECR repository and the AppRunner service are located in the same region. The service that resides in the same region as ECR will be updated automatically, but the services in other regions will not.

The documentation only mentions that automatic deployments are unsupported if ECR is located in a separate **account**.
At the very least, the documentation should be adapted to say that automatic deployments will not work if ECR is in a different region than the service.

**Describe alternatives you've considered**

* Manual deployment (tedious, error-prone)
* Disable cross-region replication, and push to each individual repository (error-prone, deployments might become out of sync)

**Additional context**

ECR private repo replication is enabled, and I see the images in the ECR repositories in all regions.

AWS Developer Support case number: 171991969200417

**Attachments**
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