Add Azure Event Grid integration with CloudEvents support

[belljun3395]

Azure Event Grid Trigger Sample

Overview

This PR adds a comprehensive Azure Event Grid trigger sample that demonstrates integration with Spring Cloud Function using CloudEvents v1.0 specification. The sample showcases event processing patterns for modern cloud-native applications.

This contribution is also related to #1279

What's Included

Core Implementation

• EventGridDemoApplication: Main Spring Boot application with two Spring Cloud Functions
  • processEvent: Processes incoming CloudEvents with detailed logging
  • createEvent: Creates CloudEvents from payload maps
• EventGridHandler: Azure Function HTTP trigger handler that supports:
  • CloudEvents v1.0 format (structured and binary mode)
  • Event Grid native format with automatic conversion
  • Webhook validation according to CloudEvents specification

Key Features

• Multi-format Support: Handles both CloudEvents and Event Grid formats seamlessly
• Webhook Validation: Implements proper Azure Event Grid subscription validation
• Binary Mode Support: Processes CloudEvents in both structured (JSON) and binary (HTTP headers) modes
• Automatic Conversion: Converts Event Grid format events to CloudEvents for consistent processing
• Comprehensive Testing: Unit tests covering validation, format detection, and event processing paths

Configuration & Deployment

• Maven configuration for Azure Functions deployment
• Local development setup with Azure Functions Core Tools
• Complete Azure resource setup scripts
• Detailed README with usage examples

Technical Implementation Details

The sample demonstrates several important patterns:

1. Event Format Detection: Automatically detects and handles different event formats based on content-type and headers
2. CloudEvents Standards Compliance: Full support for CloudEvents v1.0 specification
3. Spring Cloud Function Integration: Uses function catalog for loose coupling between Azure Functions and business logic
4. Error Handling: Graceful error handling with appropriate HTTP status codes

Testing Strategy

The implementation includes comprehensive unit tests that verify:

• Webhook validation with and without origin headers
• Event format detection (CloudEvents vs Event Grid)
• Subscription validation event handling
• Binary mode CloudEvent processing

Benefits

• Standardization: Uses CloudEvents specification for interoperability
• Flexibility: Supports multiple event formats and delivery modes
• Production Ready: Includes proper error handling, logging, and testing
• Educational Value: Demonstrates best practices for Azure Event Grid integration

This sample provides a solid foundation for developers building event-driven applications with Azure Event Grid and Spring Cloud Function.