docs: [five-c] add usage and configuration documentation #416

[tdruez]

Issues

• Issue: five-c: Create usage and configuration documentation #416

Policy Rules Reference Documentation

• New reference page reference-policy-rules.rst documenting the Policy Rules Engine concept, built-in rules, configuration, and integrations
• Built-in rules table split into policy-based and vulnerability-based categories, covering all eight rules with rule type, label, severity, and description
• Violation lifecycle explaining the detected, active, resolved, and re-activated states
• Configuration reference for the policy_rules_config JSON field with a full example and per-rule parameter details
• Evaluation triggers documenting both automatic background re-evaluation and manual re-evaluation entry points
• Webhook events documenting policy.violation_detected and policy.violation_resolved with payload descriptions, linked to the Webhook integration page
• REST API documenting the GET /api/v2/products/{uuid}/policy_violations/ endpoint and all returned fields