.NET: [Feature Branch] Add basic durable workflow support (#3648)

* Add basic durable workflow support.

* PR feedback fixes

* Add conditional edge sample.

* PR feedback fixes.

* Minor cleanup.

* Minor cleanup

* Minor formatting improvements.

* Improve comments/documentation on the execution flow.

dotnet/src/Microsoft.Agents.AI.DurableTask/Workflows/DurableWorkflowInput.cs

@@ -0,0 +1,16 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+namespace Microsoft.Agents.AI.DurableTask.Workflows;
+
+/// <summary>
+/// Represents the input envelope for a durable workflow orchestration.
+/// </summary>
+/// <typeparam name="TInput">The type of the workflow input.</typeparam>
+internal sealed class DurableWorkflowInput<TInput>
+    where TInput : notnull
+{
+    /// <summary>
+    /// Gets the workflow input data.
+    /// </summary>
+    public required TInput Input { get; init; }
+}