fix(istio): bump default Istio version to 1.30.4

[sebastiancorrea81]

Summary

• istio_base_version and istiod_version (infrastructure/commons/istio) were still pinned at 1.27.1, which reached EOL on 2026-04-07. Bumps both to 1.30.4, the latest available release (chart version matches app version across istio/base, istio/istiod, and istio/gateway on the official Istio Helm repo).
• Also bumps nullplatform/base's gateway_api_crd_ref default from v1.3.0 to v1.5.1 in the same PR: Istio 1.30's own upgrade notes document installing Gateway API CRDs at v1.5.1, and explicitly warn that upgrading Istio without also upgrading these CRDs leaves TLSRoute/ReferenceGrant invisible to istiod. Leaving the ref pinned to what 1.27 needed would reintroduce the exact version-mismatch problem fixed in fix(base): expose gateway_api_crd_ref, default to v1.3.0 for Istio 1.27 #544.

Notes for reviewers

• This is a 3-minor-version jump (1.27 → 1.28 → 1.29 → 1.30). Checked Istio's upgrade notes across that range; the only breaking changes found were unrelated to what this module configures (CNI file permissions, debug endpoint auth, sidecar statsCompression annotation removal, service namespace tie-breaking). Nothing here touches pilot.replicaCount/pilot.autoscaleMin, the only Helm values this module sets.
• Istio 1.30 supports Kubernetes 1.29–1.34 — worth confirming target clusters are in range before rolling this out.
• Did not touch nullplatform_base_helm_version (chart version) — out of scope for this PR.

Test plan

• tofu test — 6/6 passing in infrastructure/commons/istio
• tofu test — 29/29 passing in nullplatform/base
• tofu validate on both modules
• Reviewer sign-off

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