Add interceptor for unsubscriptions.

Source/MQTTnet.Server/Mqtt/MqttServerService.cs

@@ -33,6 +33,7 @@ namespace MQTTnet.Server.Mqtt
         private readonly MqttServerConnectionValidator _mqttConnectionValidator;
         private readonly IMqttServer _mqttServer;
         private readonly MqttSubscriptionInterceptor _mqttSubscriptionInterceptor;
+        private readonly MqttUnsubscriptionInterceptor _mqttUnsubscriptionInterceptor;
         private readonly PythonScriptHostService _pythonScriptHostService;
         private readonly MqttWebSocketServerAdapter _webSocketServerAdapter;
 
@@ -45,6 +46,7 @@ namespace MQTTnet.Server.Mqtt
             MqttClientUnsubscribedTopicHandler mqttClientUnsubscribedTopicHandler,
             MqttServerConnectionValidator mqttConnectionValidator,
             MqttSubscriptionInterceptor mqttSubscriptionInterceptor,
+            MqttUnsubscriptionInterceptor mqttUnsubscriptionInterceptor,
             MqttApplicationMessageInterceptor mqttApplicationMessageInterceptor,
             MqttServerStorage mqttServerStorage,
             PythonScriptHostService pythonScriptHostService,
@@ -57,6 +59,7 @@ namespace MQTTnet.Server.Mqtt
             _mqttClientUnsubscribedTopicHandler = mqttClientUnsubscribedTopicHandler ?? throw new ArgumentNullException(nameof(mqttClientUnsubscribedTopicHandler));
             _mqttConnectionValidator = mqttConnectionValidator ?? throw new ArgumentNullException(nameof(mqttConnectionValidator));
             _mqttSubscriptionInterceptor = mqttSubscriptionInterceptor ?? throw new ArgumentNullException(nameof(mqttSubscriptionInterceptor));
+            _mqttUnsubscriptionInterceptor = mqttUnsubscriptionInterceptor ?? throw new ArgumentNullException(nameof(mqttUnsubscriptionInterceptor));
             _mqttApplicationMessageInterceptor = mqttApplicationMessageInterceptor ?? throw new ArgumentNullException(nameof(mqttApplicationMessageInterceptor));
             _mqttServerStorage = mqttServerStorage ?? throw new ArgumentNullException(nameof(mqttServerStorage));
             _pythonScriptHostService = pythonScriptHostService ?? throw new ArgumentNullException(nameof(pythonScriptHostService));
@@ -178,6 +181,7 @@ namespace MQTTnet.Server.Mqtt
                 .WithConnectionValidator(_mqttConnectionValidator)
                 .WithApplicationMessageInterceptor(_mqttApplicationMessageInterceptor)
                 .WithSubscriptionInterceptor(_mqttSubscriptionInterceptor)
+                .WithUnsubscriptionInterceptor(_mqttUnsubscriptionInterceptor)
                 .WithStorage(_mqttServerStorage);
 
             // Configure unencrypted connections