[beryllw]

Purpose

Closes #4753.

Support deploying Fluss Gateway on Kubernetes as an independent Helm release connected to an existing Fluss cluster.

Brief change log

• Add a Gateway chart with backend Secret references, health probes, graceful shutdown, and optional Prometheus metrics.
• Organize the charts under helm/fluss/ and helm/fluss-gateway/.
• Update CI and release tooling to test and package both charts independently.

Tests

• 177 chart unit tests passed; strict lint passed on Helm 3.8 and 4.3.
• Validated 27 rendered resources against Kubernetes 1.19 schemas and checked packaged chart rendering.
• Website build and root Maven verification, license, and formatting checks passed in a clean source export.

Live Kubernetes deployment has not been tested.

API and Format

No REST API or storage format changes.

Source-based Fluss installation moves from ./helm to ./helm/fluss. The existing chart’s values and rendered resources remain unchanged.

Documentation

Update Helm READMEs, deployment guides, and release instructions.