Add Container Registry API tests

Issue: gitlab-org/quality/testcases#1694 (closed)

Container REST API test on preprod: #321739 (closed)

@svistas, as discussed during our sync, the only two registry API operations that are not covered/used by the GitLab Rails integration are the manifest and blob deletions:

• Deleting a manifest/image - As result, a subsequent check request should return 404 Not Found, and all tags that existed for that image/manifest should be gone as well, so they shouldn't appear in the tag list response.
• Deleting a blob. As result, a subsequent check request should return 404 Not Found.