Clean up handoff orchestration creation (#235)

- Remove Dictionary-derived types
- Add an optional name to orchestrations
- Make Handoffs based purely on AIAgent instances rather than separately provided names

dotnet/samples/GettingStarted/Orchestration/HandoffOrchestration_Intro.cs

@@ -56,11 +56,12 @@ public class HandoffOrchestration_Intro(ITestOutputHelper output) : Orchestratio
         responses.Enqueue("Order ID 321");
         responses.Enqueue("Broken item");
         responses.Enqueue("No, bye");
+
         // Define the orchestration
         HandoffOrchestration orchestration =
-            new(OrchestrationHandoffs
+            new(Handoffs
                     .StartWith(triageAgent)
-                    .Add(triageAgent, statusAgent, returnAgent, refundAgent)
+                    .Add(triageAgent, [statusAgent, returnAgent, refundAgent])
                     .Add(statusAgent, triageAgent, "Transfer to this agent if the issue is not status related")
                     .Add(returnAgent, triageAgent, "Transfer to this agent if the issue is not return related")
                     .Add(refundAgent, triageAgent, "Transfer to this agent if the issue is not refund related"))

dotnet/samples/GettingStarted/Orchestration/HandoffOrchestration_With_StructuredInput.cs

@@ -46,9 +46,9 @@ public class HandoffOrchestration_With_StructuredInput(ITestOutputHelper output)
 
         // Define the orchestration
         HandoffOrchestration orchestration =
-            new(OrchestrationHandoffs
+            new(Handoffs
                     .StartWith(triageAgent)
-                    .Add(triageAgent, dotnetAgent, pythonAgent))
+                    .Add(triageAgent, [dotnetAgent, pythonAgent]))
             {
                 LoggerFactory = this.LoggerFactory,
                 ResponseCallback = monitor.ResponseCallback,