GH-8879: Add MQTT subscription identifier

Fixes: #8879

To workaround the problem with `$share/` subscriptions the `Mqttv5PahoMessageDrivenChannelAdapter` must provide a `subscriptionIdentifier` into `MqttProperties` on `subscribe()`

* Introduce a `Mqttv5PahoMessageDrivenChannelAdapter.subscriptionIdentifierCounter` according to the MQTT specification:
> 3.8.2.1.2 Subscription Identifier: [..]The Subscription Identifier is associated with any subscription created or modified as the result of this SUBSCRIBE packet. If there is a Subscription Identifier, it is stored with the subscription. 

This one is associated with the MQTT session for the current subscriber and does not interfere into other sessions even if identifier is same from the counter.
It works because the Subscription identifier is per session and because you cannot have multiple connection with the same client ID.

**Cherry-pick to `6.2.x` & `6.1.x`**

spring-integration-mqtt/src/main/java/org/springframework/integration/mqtt/inbound/Mqttv5PahoMessageDrivenChannelAdapter.java

@@ -21,6 +21,7 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.stream.IntStream;
@@ -107,6 +108,8 @@ public class Mqttv5PahoMessageDrivenChannelAdapter
 
 	private volatile boolean readyToSubscribeOnStart;
 
+	private final AtomicInteger subscriptionIdentifierCounter = new AtomicInteger(0);
+
 	/**
 	 * Create an instance based on the MQTT url, client id and subscriptions.
 	 * @param url the MQTT url to connect.
@@ -336,8 +339,10 @@ public void addTopic(String topic, int qos) {
 				this.subscriptions.add(subscription);
 			}
 			if (this.mqttClient != null && this.mqttClient.isConnected()) {
+				MqttProperties subscriptionProperties = new MqttProperties();
+				subscriptionProperties.setSubscriptionIdentifier(this.subscriptionIdentifierCounter.incrementAndGet());
 				this.mqttClient.subscribe(new MqttSubscription[] { subscription },
-								null, null, new IMqttMessageListener[] { this::messageArrived }, new MqttProperties())
+								null, null, new IMqttMessageListener[] { this::messageArrived }, subscriptionProperties)
 						.waitForCompletion(getCompletionTimeout());
 			}
 		}
@@ -467,7 +472,11 @@ private void subscribe() {
 			IMqttMessageListener[] listeners = IntStream.range(0, mqttSubscriptions.length)
 					.mapToObj(t -> listener)
 					.toArray(IMqttMessageListener[]::new);
-			this.mqttClient.subscribe(mqttSubscriptions, null, null, listeners, new MqttProperties())
+			MqttProperties subscriptionProperties = new MqttProperties();
+			subscriptionProperties.setSubscriptionIdentifiers(IntStream.range(0, mqttSubscriptions.length)
+					.mapToObj(i -> this.subscriptionIdentifierCounter.incrementAndGet())
+					.toList());
+			this.mqttClient.subscribe(mqttSubscriptions, null, null, listeners, subscriptionProperties)
 					.waitForCompletion(getCompletionTimeout());
 			String message = "Connected and subscribed to " + Arrays.toString(mqttSubscriptions);
 			logger.debug(message);

spring-integration-mqtt/src/test/java/org/springframework/integration/mqtt/Mqttv5BackToBackTests.java

@@ -137,6 +137,22 @@ public void testSimpleMqttv5Interaction() {
 		assertThat(receive.getPayload()).isEqualTo(testPayload);
 	}
 
+	@Test
+	public void testSharedTopicMqttv5Interaction() {
+		this.mqttv5MessageDrivenChannelAdapter.addTopic("$share/group/testTopic");
+
+		String testPayload = "shared topic payload";
+		this.mqttOutFlowInput.send(
+				MessageBuilder.withPayload(testPayload)
+						.setHeader(MqttHeaders.TOPIC, "testTopic")
+						.build());
+
+		Message<?> receive = this.fromMqttChannel.receive(10_000);
+
+		assertThat(receive).isNotNull();
+		assertThat(receive.getPayload()).isEqualTo(testPayload);
+	}
+
 
 	@Configuration
 	@EnableIntegration