[ECR] [request]: Generate SOCI indexes automatically

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**Tell us about your request**
I would like for ECR to automatically generate SOCI indexes for all pushed images. This way, I do not have to change all my pipelines, and can benefit from SOCI without any additional configuration,.

**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?**
We have thousands of pipelines which build containers and changing them all to build and push SOCI indexes would be painful.

**Are you currently working around this issue?**
Changing each pipeline, but many teams don't know about benefits of SOCI.

**Additional context**
Thanks!

**Attachments**

The request concerns ECR automatically generating SOCI indexes for pushed container images, but it names no repository files, tests, or entry points. Start by researching ECR image-push behavior and SOCI index generation, then define the automatic workflow and verify that existing pipelines can benefit without configuration changes.

Written by the indexing model from the issue text.