Configuration module for Sentinel proxy

This module provides configuration parsing, validation, and hot-reload support with a focus on safety, security-first defaults, and operational clarity.

Module Organization

• [server]: Server and listener configuration
• [routes]: Route configuration and match conditions
• [upstreams]: Upstream backend configuration
• [agents]: External processing agent configuration
• [waf]: WAF (Web Application Firewall) configuration
• [observability]: Metrics, logging, and tracing configuration
• [filters]: Filter types for request/response processing
• [validation]: Configuration validation functions
• [kdl]: KDL format parsing
• [defaults]: Default embedded configuration
• [multi_file]: Multi-file configuration loading