CAMEL-23260: fix graceful shutdown for ServiceBus consumer

[Croway]

Summary

• Implement ShutdownAware in ServiceBusConsumer to defer shutdown until in-flight exchanges complete their ACK/NACK to Azure Service Bus
• Change doStop() from client.close() to client.stop() to keep the AMQP connection alive for in-flight message acknowledgement
• Add doShutdown() to close the client only after all exchanges have drained
• Track in-flight exchanges with AtomicInteger counter, decremented in try/finally blocks in onComplete()/onFailure()

Test plan

• New unit tests for deferShutdown(), getPendingExchangesSize(), doStop(), doShutdown()
• All existing 17 consumer tests continue to pass
• mvn verify passes on camel-azure-servicebus module

[github-actions]

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