[ECR] [request]: Replication Image Tag Filter

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**Tell us about your request**

I'd like to have the ability to filter images to be replicated within a repository by image tag. We currently use this for lifecycles by tagging snapshots and releases with a secondary lifecycle tag of _snapshot__IMAGE_TAG_ or _release__IMAGE_TAG_. We only want to replicate release images to our replica regions but currently, replication can only filter down based on repositories not images within a repository.

**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?**

This is currently technically possible using other methods explained below, but having this as native functionality would greatly improve our experience.

**Are you currently working around this issue?**

We are considering breaking up our repositories to having one for snapshots and one for releases of each service. The other option we're evaluating is not using ECR replication but going back to pushing our images to all enabled regions for releases only.

**Additional context**
Anything else we should know?

**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.)

Start by reviewing the ECR replication behavior described in the issue, including its current repository-only filtering and the snapshot/release tag workaround. Done would mean defining and implementing native filtering of replicated images by image tag, with behavior covering the release-only replication request.

Written by the indexing model from the issue text.