[ECR] [request]: Pull through cache support for JFrog Container Registry (jfrog.io)

### Community Note

* Please vote on this issue by adding a 👍 [reaction](https://blog.github.com/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/) to the original issue to help the community and maintainers prioritize this request
* Please do not leave "+1" or "me too" comments, they generate extra noise for issue followers and do not help prioritize the request
* If you are interested in working on this issue or have submitted a pull request, please leave a comment

**Tell us about your request**
We would like to use pull through cache with JFrog container registries with credentials.

**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?**
What outcome are you trying to achieve, ultimately, and why is it hard/impossible to do right now? What is the impact of not having this problem solved? The more details you can provide, the better we'll be able to understand and solve the problem.

**Are you currently working around this issue?**
We are currently unable to use pull through cache with jfrog.io registries as it is not yet supported as an upstream source registry.

**Attachments**

- https://jfrog.com/help/r/jfrog-artifactory-documentation/jfrog-container-registry
- https://jfrog.com/devops-tools/article/docker-hub-and-docker-registries-a-beginners-guide/

No repository files, tests, or implementation entry points are named. Start by reviewing ECR pull-through cache behavior and the linked JFrog Container Registry documentation, then determine the service and credential requirements for jfrog.io as an upstream source. Done means ECR supports authenticated pull-through caching from JFrog Container Registry.

Written by the indexing model from the issue text.