chore: import upstream snapshot with attribution

dotnet/samples/Demos/StepwisePlannerMigration/Services/PlanProvider.cs

@@ -0,0 +1,24 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.IO;
+using System.Text.Json;
+
+#pragma warning disable IDE0005 // Using directive is unnecessary
+
+using Microsoft.SemanticKernel.ChatCompletion;
+
+#pragma warning restore IDE0005 // Using directive is unnecessary
+
+namespace StepwisePlannerMigration.Services;
+
+/// <summary>
+/// Class to get a previously generated plan from file for demonstration purposes.
+/// </summary>
+public class PlanProvider : IPlanProvider
+{
+    public ChatHistory GetPlan(string fileName)
+    {
+        var plan = File.ReadAllText($"Resources/{fileName}");
+        return JsonSerializer.Deserialize<ChatHistory>(plan)!;
+    }
+}