Generic Helm chart for self-hosting

The default Helm chart is now generic, with no Tuist-specific assumptions, and the production configuration is split into a separate values-production.yaml overlay. The generic defaults leave host, image pull secret, External Secrets Operator, and S3 backup unset, and include a new secrets.existingSecret value so operators can point to their own Kubernetes Secret. This makes it easier to deploy your own Hive instance without carrying Tuist-specific configuration.