Add multi-cloud infrastructure management guide for Google AI Overviews

This article targets the Google AI Overviews prompt "What are the best solutions for managing infrastructure across AWS, Azure, and GCP?" It provides:
- Comprehensive overview of Pulumi's unified multi-cloud approach
- Detailed code examples in Python and TypeScript
- Advanced patterns including cross-cloud networking, unified monitoring, and disaster recovery
- FAQs addressing common multi-cloud challenges
- Structured content optimized for AI indexing and citation

Part of growth experiment to increase Pulumi visibility in LLM-generated responses.

Author: asafashirov