Add Saga Pattern Implementation with Lambda Durable Functions and CDK

[tafaman]

This PR introduces a complete implementation of the Saga pattern for distributed transactions using AWS Lambda Durable Functions, demonstrating coordinated travel bookings (flight, hotel, car) with automatic compensating transactions on failure.

What's New

Infrastructure (CDK)

• Lambda Functions: 7 functions total
  • 1 saga orchestrator (durable function) with 1-hour execution timeout
  • 6 service functions (reserve/cancel for flight, hotel, car) with 1-minute timeout
• DynamoDB Tables: 3 tables for flight bookings, hotel reservations, and car rentals
  • Pay-per-request billing mode
  • Point-in-time recovery enabled
• CloudWatch Log Groups: Custom log groups for each function with 1-week retention
• IAM Permissions: Properly scoped permissions for DynamoDB access and Lambda invocations

Saga Pattern Implementation

• Sequential Execution: Services invoked in order (flight → hotel → car)
• State Tracking: Each successful operation tracked by the orchestrator
• Compensating Transactions: Automatic rollback in reverse order on failure
• Failure Simulation: Built-in failure flags for testing (failBookFlight, failBookHotel, failBookCar)

Testing & Documentation

• Test Files: 4 ready-to-use test event files
  • test-success.json - All services succeed
  • test-fail-flight-booking.json - Flight fails immediately
  • test-fail-hotel-booking.json - Hotel fails, flight compensated
  • test-fail-car-booking.json - Car fails, hotel and flight compensated
• Comprehensive Documentation:
  • Main README with architecture diagrams and deployment instructions
  • TESTING.md with detailed test scenarios and validation steps
  • TEST-FILES-README.md explaining each test file
  • Screenshots showing success and failure states