[ECR] [request]: Anonymous pulls from private registries.

### Community Note

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**Tell us about your request**
What do you want us to build?
Allow anonymous pulls from private registries. I'd like to be able to create privatelink endpoints against a registry that doesn't require authentication in support of airgapped environments.

**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.

When building vanilla Kubernetes clusters imagePullSecrets for the private registries have to be pre-staged. This is especially tedious for temporary pipeline clusters.

**Are you currently working around this issue?**
How are you currently solving this problem?
Not utilizing ECR but hosted container registries on EC2 instances.

**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.)

No files, tests, or code entry points are mentioned; start by reviewing the ECR request and its PrivateLink and air-gapped-environment context. Done means supporting anonymous pulls from private registries so temporary Kubernetes clusters do not need pre-staged imagePullSecrets.

Written by the indexing model from the issue text.