Refactor "Deploying a GreptimeDB Cluster with Frontend Groups" to Use Helm-Based Configuration

The current "Deploying a GreptimeDB Cluster with Frontend Groups" guide relies on Kubernetes YAML manifests.

To ensure consistency and maintainability, this document should be refactored to:
- Replace raw YAML with a values.yaml-based Helm deployment.
- Align with the structure and style used in other Helm-based deployment guides.
