fix(e2e): detect gateway workload for readyz port-forward

[elezar]

Summary

Make the Kubernetes E2E readyz health port-forward work with both StatefulSet-backed and Deployment-backed gateway releases. This preserves the existing readyz coverage while extracting the generally applicable workload discovery from the HA work in #1868.

Related Issue

Related to #1868. Replaces the minimal proof-of-life approach from closed PR #2198 as a standalone current-main change.

Changes

• Discover the installed gateway workload as either statefulset/<release> or deployment/<release> at runtime.
• Fail explicitly when neither supported workload exists.
• Use the discovered workload for the named health port-forward in both database-scenario and single-install E2E paths.
• Preserve the existing readyz_health Rust test and its Kubernetes feature registration.

Testing

• bash -n e2e/with-kube-gateway.sh
• git diff --check
• Static verification that e2e/rust/tests/readyz_health.rs and its e2e-kubernetes test target remain present
• mise run pre-commit completes (the Nix-backed run timed out after five minutes during a cold Rust workspace test build; all reported completed checks passed, including Helm lint, formatting, licensing, Python lint/type/tests, Markdown lint, and packaging checks)
• Kubernetes E2E (not run locally)

Checklist

• Follows Conventional Commits
• Commit is signed off (DCO)
• Change is limited to readyz workload discovery and port-forward selection

[copy-pr-bot]

Auto-sync is disabled for draft pull requests in this repository. Workflows must be run manually.

Contributors can view more details about this message here.