.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.AppHost/Program.cs

@@ -0,0 +1,26 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using AgentWebChat.AppHost;
+
+var builder = DistributedApplication.CreateBuilder(args);
+
+var azOpenAiResource = builder.AddParameterFromConfiguration("AzureOpenAIName", "AzureOpenAI:Name");
+var azOpenAiResourceGroup = builder.AddParameterFromConfiguration("AzureOpenAIResourceGroup", "AzureOpenAI:ResourceGroup");
+var chatModel = builder.AddAIModel("chat-model").AsAzureOpenAI("gpt-4o", o => o.AsExisting(azOpenAiResource, azOpenAiResourceGroup));
+
+var cosmosDbResource = builder.AddParameterFromConfiguration("CosmosDbName", "CosmosDb:Name");
+var cosmosDbResourceGroup = builder.AddParameterFromConfiguration("CosmosDbResourceGroup", "CosmosDb:ResourceGroup");
+var cosmos = builder.AddAzureCosmosDB("agent-web-chat-cosmosdb").RunAsExisting(cosmosDbResource, cosmosDbResourceGroup);
+
+var stateDb = cosmos.AddCosmosDatabase("actor-state-db");
+
+var agentHost = builder.AddProject<Projects.AgentWebChat_AgentHost>("agenthost")
+        .WithReference(chatModel)
+        .WithReference(cosmos).WaitFor(cosmos);
+
+builder.AddProject<Projects.AgentWebChat_Web>("webfrontend")
+    .WithExternalHttpEndpoints()
+    .WithReference(agentHost)
+    .WaitFor(agentHost);
+
+builder.Build().Run();