feat: Implement `JetStream` Source-to-Sink Example with Flink

[somratdutta]

• Added a JetStream source-to-sink example integrating NATS JetStream with Apache Flink.
• Configured:
  • JetStream stream and consumer creation for message flow.
  • Flink environment with JetStream source and sink.
• Implemented test message publishing to the source subject.
• Subscribed to the sink subject to verify message flow.
• Included proper cleanup:
  • Unsubscribing from dispatcher.
  • Deleting the JetStream stream after execution.
  • Closing NATS connection and Flink environment gracefully.
• Set up acknowledgment policy (AckPolicy.All) for batch acknowledgment.
• Enabled checkpointing and restart strategy for Flink fault tolerance.

This example demonstrates a complete message processing pipeline from source to sink using JetStream and Flink.