Add AWS MSK Cluster Monitoring Dashboard (OTLP v1)

[blessuselessk]

Summary

• Adds a comprehensive AWS MSK (Managed Streaming for Apache Kafka) cluster monitoring dashboard using CloudWatch metrics collected via OpenTelemetry
• Uses the SigNoz Query Builder (not PromQL) with aws_kafka_* metric names matching the CloudWatch AWS/Kafka namespace convention
• 24 panels organized into 5 collapsible sections: Broker Metrics, Topic Metrics, Partition Metrics, Consumer Metrics, and AWS CloudWatch Metrics
• Dashboard variables for cluster_name, broker_id (multi-select), and deployment.environment

Panels

Broker Metrics (8 panels): CPU User/System, Memory Used/Free, Disk Usage (Data Logs), Disk Throughput (Read/Write), Network RX/TX Packets

Topic Metrics (4 panels): Bytes In/Out Per Second, Messages In Per Second, Produce Total Time Mean

Partition Metrics (5 panels): Under-Replicated Partitions, Offline Partitions Count, Active Controller Count, Partition Count, Leader Count

Consumer Metrics (2 panels): Consumer Lag (Sum Offset Lag), Estimated Max Time Lag

AWS Metrics (5 panels): Burst Balance, CPU Credit Usage, Traffic Shaping, Connection Count, Heap Memory After GC

Key Differentiators from Other PRs

• Uses Query Builder (preferred per CONTRIBUTING.md) instead of PromQL
• Uses correct aws_kafka_* CloudWatch metric naming (matching ElastiCache/RDS pattern in this repo), not JMX/Prometheus metrics
• Follows the exact schema of recently-merged dashboards (panelMap sections, row panels, v4 format)
• All metric names verified against official AWS MSK CloudWatch documentation
• Includes complete OTel collector configuration in README

Fixes SigNoz/signoz#6036

Test plan

• Import dashboard JSON into SigNoz instance
• Verify JSON parses correctly (validated with python3 -m json.tool)
• Confirm all 29 layout entries match 29 widget IDs
• Confirm all 24 graph panels are grouped under their respective panelMap sections
• Verify dashboard variables populate when aws_kafka_* metrics are present
• Verify panel queries render correctly with CloudWatch MSK metrics