[Code Update - Chapter 12] Code update for MP GraphQL 2.0

[ttelang]

This PR adds comprehensive code examples for Chapter 12 of the MicroProfile Tutorial, demonstrating implementations of MicroProfile GraphQL 2.0 specifications.

What's Included

A complete GraphQL Catalog Service application showcasing:

Core Features:

• GraphQL API with queries and mutations for product catalog management
• Field Resolvers using @Source annotation for on-demand relationship resolution
• Computed Fields for derived data (tax calculations, price categories, stock status)
• Custom Exception Handling with GraphQL-compliant error responses
• MicroProfile Config Integration for externalized configuration

Examples:

1. Product Management

   • Query operations: products, product(id), searchProducts, productCount, averagePrice, categories
   • Mutations: createProduct, updateProduct, deleteProduct
   • Complex queries demonstrating variables, fragments, and aliases

2. Advanced GraphQL Patterns

   • Field resolvers: reviews, topReviews(limit), averageRating
   • Computed fields: priceWithTax, priceCategory, availabilityStatus
   • Polymorphic queries using the Identifiable interface
   • Error handling with ProductNotFoundException and InsufficientStockException

3. Supporting Services

   • ProductService - Business logic layer
   • ReviewService - Review operations and aggregations
   • PricingService - Discount and pricing calculations
   • InventoryService - Stock level management
   • OrderService - Order creation and tracking

4. Data Layer

   • In-memory repositories with sample data initialization
   • Product and Review entities with GraphQL annotations
   • Input types for mutations

5. Configuration & Documentation

   • Liberty server configuration for Open Liberty runtime
   • Comprehensive README with API documentation
   • Example GraphQL queries (basic queries, mutations, variables, fragments)
   • Schema introspection examples
   • curl command examples for testing