added LogId to options and use it to create logging scope

MQTTnet.Core/Client/IMqttClientOptions.cs

@@ -6,6 +6,11 @@ namespace MQTTnet.Core.Client
     public interface IMqttClientOptions
     {
         string ClientId { get; }
+
+        /// <summary>
+        /// The LogId is used to create a scope to correlate logging. If no value is provided the ClientId is used instead 
+        /// </summary>
+        string LogId { get; }
         IMqttClientCredentials Credentials { get; }
         bool CleanSession { get; }
         MqttApplicationMessage WillMessage { get; }

MQTTnet.Core/Client/MqttClient.cs

@@ -55,7 +55,7 @@ namespace MQTTnet.Core.Client
 
                 _adapter = _communicationAdapterFactory.CreateClientMqttCommunicationAdapter(options);
 
-                _scopeHandle = _logger.BeginScope(options.ClientId);
+                _scopeHandle = _logger.BeginScope(options.LogId ?? options.ClientId);
                 _logger.LogTrace("Trying to connect with server.");
                 await _adapter.ConnectAsync(_options.CommunicationTimeout).ConfigureAwait(false);
                 _logger.LogTrace("Connection with server established.");

MQTTnet.Core/Client/MqttClientOptions.cs

@@ -9,6 +9,9 @@ namespace MQTTnet.Core.Client
 
         public string ClientId { get; set; } = Guid.NewGuid().ToString("N");
 
+        /// <inheritdoc />
+        public string LogId { get; set; }
+
         public bool CleanSession { get; set; } = true;
 
         public IMqttClientCredentials Credentials { get; set; } = new MqttClientCredentials();