ci(kubernetes): expose e2e test selection

[elezar]

Summary

Expose optional Rust test-target and Cargo feature selection through the reusable Kubernetes e2e workflow. Empty inputs preserve the current test suite and the existing OPENSHELL_E2E_KUBERNETES_FEATURES developer-facing contract.

This remains a draft because main has no independent caller that consumes the new inputs yet. The intended first consumer is currently part of #1868; this PR deliberately does not add HA tests or callers.

Related Issue

Extracted from #1868 for independent review.

Changes

• Add optional test-name and kubernetes-features workflow_call inputs.
• Forward the inputs through OPENSHELL_E2E_KUBE_TEST and the existing OPENSHELL_E2E_KUBERNETES_FEATURES variable.
• Keep empty values behavior-neutral by relying on the existing shell defaults.

Testing

• mise run pre-commit passes
  • Attempted inside the Nix environment after pre-syncing Python dependencies. The five-minute run timed out during parallel cold Rust builds; remaining Rust processes were resource-killed with SIGKILL, not failed assertions. Completed format, license, Helm, Markdown, Python lint/typecheck/tests, packaging, and install-script checks passed.
• Parsed the workflow YAML and asserted both input defaults and environment wiring.
• bash -n e2e/rust/e2e-kubernetes.sh
• Verified unset, empty, and explicit OPENSHELL_E2E_KUBERNETES_FEATURES expansion.
• E2E tests run (no independent caller on main yet)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)

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[elezar]

gator-agent

Maintainer Approval Needed

Gator validation and PR monitoring are complete for head 92665892cac85be61b8e337d3cff484df5793549.

Validation: This maintainer-authored PR is project-valid as a narrow CI/Kubernetes e2e workflow improvement extracted from #1868. Duplicate search found no active overlapping PR.

Head SHA: 92665892cac85be61b8e337d3cff484df5793549

Review: Independent principal engineer review found no blocking correctness, security, maintainability, or missing-test findings.

Docs: Not needed; this changes a reusable CI workflow interface, not direct user-facing Fern docs.

Checks: Required gates are green: Branch Checks, Helm Lint, E2E gate, GPU E2E gate, and DCOAssistant.

E2E: No additional test:* label applied. This change exposes existing script controls and preserves the default workflow behavior when the new inputs are empty.

Human maintainer approval is now required.