Add Kong Gateway monitoring dashboard

[sivaadityacoder]

Fixes #6028

Added Kong Gateway monitoring dashboard with the following features:

Dashboard Sections:

• General Overview: Total requests and active connections
• Request Metrics: Request rate and status code distribution
• Latency Tracking: Average latency plus p50, p90, p99 percentiles
• Error Monitoring: Error rate percentage over time
• Traffic Analysis: Incoming and outgoing bandwidth
• Resource Usage: CPU, memory, and pod restart tracking

Metrics Covered:

• HTTP requests and response codes
• Latency percentiles
• Network bandwidth
• Resource consumption
• Connection metrics

Setup:
The dashboard uses Kong Prometheus plugin metrics. Setup instructions are in the README.

Testing:
Dashboard queries follow standard PromQL patterns used by Kong OpenTelemetry metrics. Compatible with Kong 3.x deployments using the Prometheus plugin.

All panels include proper variable support for namespace and service filtering.