.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/DurableOptions.cs

@@ -0,0 +1,31 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Diagnostics;
+using Microsoft.Agents.AI.DurableTask.Workflows;
+
+namespace Microsoft.Agents.AI.DurableTask;
+
+/// <summary>
+/// Provides configuration options for durable agents and workflows.
+/// </summary>
+[DebuggerDisplay("Workflows = {Workflows.Workflows.Count}, Agents = {Agents.AgentCount}")]
+public sealed class DurableOptions
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="DurableOptions"/> class.
+    /// </summary>
+    internal DurableOptions()
+    {
+        this.Workflows = new DurableWorkflowOptions(this);
+    }
+
+    /// <summary>
+    /// Gets the configuration options for durable agents.
+    /// </summary>
+    public DurableAgentsOptions Agents { get; } = new();
+
+    /// <summary>
+    /// Gets the configuration options for durable workflows.
+    /// </summary>
+    public DurableWorkflowOptions Workflows { get; }
+}