Add integration example with Unleash

[hirotask]

Summary

Add a sample demonstrating how to integrate the flagly with Unleash, the feature management service.

Motivation

Unleash is a widely used feature flag service, and providing an integration example will help users quickly adopt flagly in real-world environments. Without clear guidance, users may struggle to connect flagly with their application logic.

Definition of done

• A working integration example with Unleash is added in example directory.
• The example demonstrates how to fetch and evaluate feature flags.
• Required configuration (e.g., API URL, app name, instance ID) is documented with the code comments.
• The example is tested and reproducible.

Proposed approach

1. Add a sample implementation using the Unleash client SDK.
2. Provide a configuration example (e.g., environment variables or YAML).
3. Demonstrate basic usage such as:
   • Initializing the Unleash client
   • Fetching feature flags
   • Evaluating a flag
4. Include a minimal runnable example or snippet.
5. Ensure compatibility with the existing project structure.

Additional context

N/A

Related issues

N/A