refactor(grafana): migrate dashboard provisioning to opentofu and support multi-host metrics

[victoriacheng15]

Summary

Migrate Grafana dashboard provisioning from Kubernetes ConfigMaps to OpenTofu for improved declarative management and state tracking. Additionally, refactor the homelab monitoring dashboard queries to dynamically support multiple hosts instead of hardcoding a single server.

List of Changes

• Infrastructure as Code (OpenTofu): Integrate the Grafana Terraform provider to manage folders and dashboards directly, eliminating reliance on Helm-mounted ConfigMaps.
• Grafana Configuration: Enable dashboard editing and remove deprecated ConfigMap volume mounts in Helm values to support API-based provisioning.
• Observability (Dashboards): Update the homelab-monitoring dashboard SQL queries to partition by host, enabling multi-node telemetry visualization out of the box.

Verification

• Verify tofu apply successfully creates the Grafana folder and dashboards.
• Log into Grafana and ensure both Homelab Monitoring and Reading Analytics dashboards load correctly without errors.
• Confirm Homelab Monitoring panels display multi-node metrics via the new partition transformations.