GH-8879: Add MQTT subscription identifier

Fixes: #8879

To work around 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`**
# Conflicts:
#	spring-integration-mqtt/src/main/java/org/springframework/integration/mqtt/inbound/Mqttv5PahoMessageDrivenChannelAdapter.java

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2021-2023 the original author or authors.
+ * Copyright 2021-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@
 
 import java.util.Arrays;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.stream.IntStream;
 
 import org.eclipse.paho.mqttv5.client.IMqttAsyncClient;
@@ -96,6 +97,8 @@ public class Mqttv5PahoMessageDrivenChannelAdapter
 
 	private volatile boolean readyToSubscribeOnStart;
 
+	private final AtomicInteger subscriptionIdentifierCounter = new AtomicInteger(0);
+
 	public Mqttv5PahoMessageDrivenChannelAdapter(String url, String clientId, String... topic) {
 		super(url, clientId, topic);
 		Assert.hasText(url, "'url' cannot be null or empty");
@@ -266,8 +269,10 @@ public void addTopic(String topic, int qos) {
 		try {
 			super.addTopic(topic, qos);
 			if (this.mqttClient != null && this.mqttClient.isConnected()) {
+				MqttProperties subscriptionProperties = new MqttProperties();
+				subscriptionProperties.setSubscriptionIdentifier(this.subscriptionIdentifierCounter.incrementAndGet());
 				this.mqttClient.subscribe(new MqttSubscription[] { new MqttSubscription(topic, qos) },
-								null, null, new IMqttMessageListener[] { this::messageArrived }, new MqttProperties())
+								null, null, new IMqttMessageListener[] { this::messageArrived }, subscriptionProperties)
 						.waitForCompletion(getCompletionTimeout());
 			}
 		}
@@ -399,6 +404,10 @@ private void subscribe() {
 			IMqttMessageListener[] listeners = IntStream.range(0, topics.length)
 					.mapToObj(t -> listener)
 					.toArray(IMqttMessageListener[]::new);
+			MqttProperties subscriptionProperties = new MqttProperties();
+			subscriptionProperties.setSubscriptionIdentifiers(IntStream.range(0, topics.length)
+					.mapToObj(i -> this.subscriptionIdentifierCounter.incrementAndGet())
+					.toList());
 			this.mqttClient.subscribe(subscriptions, null, null, listeners, new MqttProperties())
 					.waitForCompletion(getCompletionTimeout());
 			String message = "Connected and subscribed to " + Arrays.toString(topics);

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

@@ -134,6 +134,22 @@ 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