Add tutorial for service introspection (#1266)

This PR adds comprehensive documentation for service introspection functionality in rclnodejs. The tutorial covers how to use ROS 2's service introspection feature to monitor and debug service interactions by observing real-time request/response data.

- Introduces service introspection concepts and capabilities for monitoring ROS 2 service calls
- Provides detailed examples showing different introspection states (OFF, METADATA, CONTENTS) and their use cases
- Includes advanced usage patterns like performance analysis and best practices for production deployment

Fix: #1265

Author: minggangw