docs: Add comprehensive SBOM validation guide

- Add new validation.rst documentation covering validation workflows
- Include practical examples for JSON and XML validation
- Document error handling patterns with ValidationError inspection
- Add multi-version support examples (CycloneDX 1.2-1.6)
- Provide production integration examples (FastAPI)
- Include best practices for validation in production systems
- Add validation.rst to documentation index

Addresses #708

Author: saquibsaifee

docs/index.rst

@@ -45,6 +45,7 @@ If you're looking for a CycloneDX tool to run to generate (SBOM) software bill-o
    install
    architecture
    examples
+   validation
    contributing
    support
    changelog