Deprecate support for Kubernetes 1.27 and 1.28

Summary

K8s 1.27 and 1.28 are EOL. We can deprecate support for both versions.

Acceptance Criteria

• Remove 1.27 and 1.28 cluster-tests from CI (we can keep kubeconform tests for now)
• Move 1.27 and 1.28 to Deprecated in doc/installation/cloud/index.md (not Unsupported per our support policy)
• Backport the CI changes to the latest three stable branches
• Decommission the 1.27 and 1.28 cluster