.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/WorkflowExecutorInfo.cs

@@ -0,0 +1,29 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using Microsoft.Agents.AI.Workflows;
+
+namespace Microsoft.Agents.AI.DurableTask.Workflows;
+
+/// <summary>
+/// Represents an executor in the workflow with its metadata.
+/// </summary>
+/// <param name="ExecutorId">The unique identifier of the executor.</param>
+/// <param name="IsAgenticExecutor">Indicates whether this executor is an agentic executor.</param>
+/// <param name="RequestPort">The request port if this executor is a request port executor; otherwise, null.</param>
+/// <param name="SubWorkflow">The sub-workflow if this executor is a sub-workflow executor; otherwise, null.</param>
+internal sealed record WorkflowExecutorInfo(
+    string ExecutorId,
+    bool IsAgenticExecutor,
+    RequestPort? RequestPort = null,
+    Workflow? SubWorkflow = null)
+{
+    /// <summary>
+    /// Gets a value indicating whether this executor is a request port executor (human-in-the-loop).
+    /// </summary>
+    public bool IsRequestPortExecutor => this.RequestPort is not null;
+
+    /// <summary>
+    /// Gets a value indicating whether this executor is a sub-workflow executor.
+    /// </summary>
+    public bool IsSubworkflowExecutor => this.SubWorkflow is not null;
+}