ACR Cache support for Chainguard Registry

**What is the problem you're trying to solve**
As a Chainguard product manager, I am concerned with my customers being able to consume our container images in Azure environments with low friction. Many Chainguard customers use Azure as their primary or only cloud; today many of these customers rely on inefficient processes to consume our images - either mirroring their entire registry or consuming our container images directly from Chainguard registry, bypassing ACR.

**Describe the solution you'd like**
I would like ACR to support image caching from Chainguard Registry.

The issue names Azure Container Registry (ACR) and Chainguard Registry but mentions no files, tests, or entry points. Start by reviewing how ACR image caching is currently configured and define the requirements for Chainguard Registry support; done means customers can cache Chainguard container images through ACR.

Written by the indexing model from the issue text.