e2e/image: add private registry pull/push regression test

[AryanSharma9917]

• fixes: Add e2e test for authorized pull/push #5965

Summary

• add authenticated private-registry service to the e2e compose stack
• add fixture auth config for private-registry:5001
• add TestPullPushPrivateRepository to verify unauthenticated pull/push fails and authenticated pull/push succeeds
• add htpasswd test credentials for the private registry

Context

• regression coverage for private repository auth behavior
• refs Unable to pull image from private repository after updating docker-ce-cli to 28.0.3 #5963, Add e2e test for authorized pull/push #5965

Notes

• change is limited to e2e test infrastructure and tests; no production CLI behavior changes

[AryanSharma9917]

Hi @vvoland , could someone please help approve the workflow runs for this PR and take a quick review pass when possible? Thanks in advance!

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[vvoland]

Thanks @AryanSharma9917!

I approved the workflows

[thaJeztah]

=== Failed
=== FAIL: e2e/image TestPullPushPrivateRepository (1.57s)
    private_test.go:37: assertion failed: expression is false: strings.Contains(output, "requested access to the resource is denied") || strings.Contains(output, "no basic auth credentials") || strings.Contains(output, "unauthorized") || strings.Contains(output, "authentication required"): The push refers to repository [private-registry:5001/private/alpine]
        Get "http://private-registry:5001/v2/": dial tcp: lookup private-registry on 127.0.0.11:53: server misbehaving
        
    private_test.go:43: assertion failed: 
        Command:  docker push private-registry:5001/private/alpine:test-private-pull-push
        ExitCode: 1
        Error:    exit status 1
        Stdout:   The push refers to repository [private-registry:5001/private/alpine]
        
        Stderr:   Get "http://private-registry:5001/v2/": dial tcp: lookup private-registry on 127.0.0.11:53: server misbehaving
        
        
        Failures:
        ExitCode was 1 expected 0
        Expected no error

[AryanSharma9917]

Hi @vvoland, @thaJeztah ,

There were some failing checks earlier, and I’ve addressed those issues in the latest update. I’ve pushed the fixes would appreciate it if you could take another look.

Since I’ve pushed updates, could the workflows be approved/triggered again so the checks can run?

Thanks!

[lohitkolluri]

Per @vvoland's note on #5965, carrying this forward in #7007 with a compose volume path fix for the CI DNS failures. Happy to close #7007 and push here instead if you prefer to keep this PR.