Add new PowerShell project

Source/MQTTnet.PowerShell/Cmdlets/SubscribeMqttTopicCmdlet.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 System.Management.Automation;
+
+namespace MQTTnet.PowerShell.Cmdlets;
+
+[Cmdlet("Subscribe", "MqttTopic")]
+[OutputType(typeof(MqttClientSubscribeResult))]
+public class SubscribeMqttTopicCmdlet : PSCmdlet
+{
+    [Parameter]
+    public int QoS { get; set; } = 0;
+
+    [Parameter(Mandatory = true, ValueFromPipeline = true)]
+    public required MqttSession Session { get; set; }
+
+    [Parameter(Mandatory = true)]
+    public required string Topic { get; set; }
+
+    protected override void ProcessRecord()
+    {
+        var topicFilter = new MqttTopicFilterBuilder().WithTopic(Topic).Build();
+
+        var response = Session.Client.SubscribeAsync(topicFilter).GetAwaiter().GetResult();
+
+        WriteObject(response);
+    }
+}