Add comprehensive documentation on handling system failures

[Copilot]

This PR addresses the question "How do you handle the failure when source system is down?" by creating comprehensive documentation that covers all aspects of system resilience and fault tolerance.

What's Added

New Documentation Structure

• Created a topics/ directory to organize learning content in this dev journal
• Added topics/handling-system-failures.md - a detailed 7,500+ character guide covering system failure handling strategies

Comprehensive Coverage

The documentation includes practical guidance on:

• Failure Types: Complete outages, partial degradation, and intermittent failures
• Core Patterns: Circuit breakers, retry mechanisms with exponential backoff, and fallback strategies
• Resilience Strategies: Graceful degradation, health checks, load balancing, and data persistence
• Implementation Patterns: Bulkhead, timeout, and rate limiting patterns
• Monitoring & Observability: Key metrics, alerting strategies, and logging best practices
• Testing: Chaos engineering and disaster recovery approaches
• Communication: Internal and external communication during outages

Updated Repository Structure

• Enhanced README.md with a "Topics Covered" section that provides organized access to learning content
• Established a scalable structure for future learning topics in this dev journal

This creates a valuable reference for understanding how to build resilient systems that gracefully handle source system failures, covering everything from basic retry logic to advanced chaos engineering practices.

Fixes #5.

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