.NET: Add agent hosting package and update sample (#296)

* Add agent hosting package and update sample

* Review feedback and cleanup

* Include the narrator

* wip

* wip

* Remove workaround for empty state writes.

* Handle changes to AgentThread.

* One more.

* Fix.

---------

Co-authored-by: Aditya Mandaleeka <adityam@microsoft.com>

dotnet/samples/AgentWebChat/AgentWebChat.Web/Program.cs

@@ -0,0 +1,43 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using AgentWebChat.Web;
+using AgentWebChat.Web.Components;
+using Microsoft.Extensions.AI.Agents.Runtime;
+
+var builder = WebApplication.CreateBuilder(args);
+
+// Add service defaults & Aspire client integrations.
+builder.AddServiceDefaults();
+
+// Add services to the container.
+builder.Services.AddRazorComponents()
+    .AddInteractiveServerComponents();
+
+builder.Services.AddOutputCache();
+
+builder.Services.AddHttpClient<IActorClient, HttpActorClient>(client => client.BaseAddress = new("https+http://agenthost"));
+builder.Services.AddHttpClient<AgentDiscoveryClient>(client => client.BaseAddress = new("https+http://agenthost"));
+
+var app = builder.Build();
+
+if (!app.Environment.IsDevelopment())
+{
+    app.UseExceptionHandler("/Error", createScopeForErrors: true);
+    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
+    app.UseHsts();
+}
+
+app.UseHttpsRedirection();
+
+app.UseAntiforgery();
+
+app.UseOutputCache();
+
+app.MapStaticAssets();
+
+app.MapRazorComponents<App>()
+    .AddInteractiveServerRenderMode();
+
+app.MapDefaultEndpoints();
+
+app.Run();