Add new PowerShell project

Source/MQTTnet.PowerShell/MqttMessage.cs

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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using MQTTnet.Packets;
+
+namespace MQTTnet.PowerShell;
+
+public class MqttMessage
+{
+    public required string? ContentType { get; init; }
+    public required string Payload { get; init; }
+    public int QoS { get; init; }
+    public required byte[] RawPayload { get; init; }
+    public string? ResponseTopic { get; init; }
+    public bool Retain { get; init; }
+    public required string Topic { get; init; }
+    public required List<MqttUserProperty>? UserProperties { get; init; }
+}