Migrate upstream Helm chart source to blob.istio.io

General MR

Summary

This fix addresses Istio retiring its GCP-hosted release infrastructure by December 2026: https://istio.io/latest/blog/2026/retirement-of-gcp/#helm-charts-and-other-release-artifacts

Migrates the upstream Helm chart source off the retiring Istio GCP endpoint (istio-release.storage.googleapis.com) to https://blob.istio.io/istio-release/charts:

• Updated the upstream dependency repository in chart/Chart.yaml and bumped the chart version to 1.30.4-bb.1
• Regenerated chart/Chart.lock against the new endpoint
• Updated registryUrlTemplate in renovate.json so Renovate detects releases from the new location (required for 1.31+)
• CHANGELOG entry and regenerated README

Deployed clusters are unaffected — the gateway-1.30.4.tgz pulled from the new endpoint is byte-identical to the vendored chart, so chart/charts/ is unchanged.

Relevant logs/screenshots

helm dependency update ./chart
# Downloading gateway from repo https://blob.istio.io/istio-release/charts
# succeeds; vendored tarballs unchanged
grep -r istio-release.storage.googleapis.com .
# no matches

Linked Issue

#95 (closed)

Upgrade Notices

N/A