Generic Helm chart plus production overlay for self-hosting

Self-hosted operators can now use the generic Helm chart without Tuist-specific assumptions. Defaults are vendor-neutral, and an optional values-production.yaml overlay carries the Tuist production configuration. A secrets.existingSecret value lets you bring your own Kubernetes Secret. This makes the chart usable out of the box for any team deploying Hive, while still supporting the Tuist instance workflow.