Add comprehensive drop statistics comparison documentation

[Copilot]

This PR adds documentation comparing Retina's drop statistics with other OSS monitoring tools, specifically addressing the need to understand differences between Retina's approach and traditional tools like node_exporter.

What's Added

New Documentation

• docs/03-Metrics/drop-statistics-comparison.md - Comprehensive comparison document covering:
  • Retina's dual approach: eBPF-based drops vs interface-level drops
  • Node exporter's interface statistics approach
  • Feature comparison table with capabilities and limitations
  • Migration guidance from node_exporter to Retina
  • Best practices and use case recommendations

Key Comparisons Covered

Feature	Retina eBPF	Retina LinuxUtil	Node Exporter
Data Source	eBPF hooks	ethtool/netstat	/proc/net/dev
Drop Reasons	✅ Specific reasons	✅ TCP-specific	❌ Generic only
Pod Context	✅ Advanced mode	❌	❌
Real-time	✅	❌ Polling	❌ Polling

Cross-References Added

• Updated metrics intro page to link to the new comparison
• Added references from dropreason and linuxutil plugin documentation
• Integrated with existing documentation structure

Technical Details

The documentation explains how:

• Node exporter provides node_network_receive_drop_total and node_network_transmit_drop_total from interface statistics
• Retina's linuxutil plugin offers similar interface-level drops plus TCP-specific drops from netstat
• Retina's dropreason plugin provides unique eBPF-based drop detection with specific reasons like IPTABLE_RULE_DROP, TCP_CONNECT_BASIC, etc.

Example Usage Scenarios

# Retina: See specific iptables rule drops by pod
networkobservability_drop_count{reason="IPTABLE_RULE_DROP", source_namespace="production"}

# Node Exporter: Only see total interface drops
rate(node_network_receive_drop_total[5m])

This addresses the specific request to compare Retina's drops with node_exporter's ethtool/netstat-based approach while highlighting Retina's enhanced capabilities for Kubernetes environments.

Fixes #1681.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://api.github.com/repos/microsoft/retina/releases/latest
  • Triggering command: curl -s REDACTED (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

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