Add new PowerShell project

Source/MQTTnet.PowerShell/Cmdlets/RegisterMqttMessageHandlerCmdlet.cs

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+using System.Management.Automation;
+using System.Management.Automation.Runspaces;
+
+namespace MQTTnet.PowerShell.Cmdlets;
+
+[Cmdlet(VerbsLifecycle.Register, "MqttMessageHandler")]
+public class RegisterMqttMessageHandlerCmdlet : PSCmdlet
+{
+    [Parameter(Mandatory = true, ValueFromPipeline = true)]
+    public required MqttSession Session { get; set; }
+
+    [Parameter(Mandatory = true)]
+    public ScriptBlock? Action { get; set; }
+
+    protected override void ProcessRecord()
+    {
+        EventHandler<MqttMessage> handler = (s, e) =>
+        {
+            //throw new NotImplementedException();
+            //InvokeCommand.InvokeScript(Action, false, PipelineResultTypes.Output, null, new object[] { e.Topic, e.Payload });
+        };
+
+        Session.MessageReceived += handler;
+        WriteObject($"Handler registered for MQTT messages on session.");
+    }
+}