feat: add CloudNativePG monitoring dashboard

[jay77721]

Description

Adds a monitoring dashboard for CloudNativePG (PostgreSQL operator for Kubernetes).

Panels

• Cluster Health: Instance Status, Uptime
• Connections: Connections by State, Max Connections
• Database: Size, Transactions Committed
• Replication: Lag (seconds & bytes)
• WAL Archiving: Archived Count, Failures
• Resources: CPU Usage, Memory Working Set
• Checkpoints: Buffers Written, Write Time
• Operations: Deadlocks, Tuple Operations
• Locks & Temp: Active Locks, Temp Bytes

Variables

• cnpg_cluster, cnpg_instance, k8s.node.name

Metrics Source

Metrics collected via CloudNativePG metrics exporter (cnpg_collector_*).

References

Related to SigNoz issue: SigNoz/signoz#7875
CNPG Grafana dashboard: https://github.com/cloudnative-pg/grafana-dashboards