.NET: Adding Image Multi Modality Sample (#688)

* Adding Multi Modal Sample

* Address typos

* Update sample to Azure OpenAI

* Update readme

* Update readme

* Update readme

* Use thread

dotnet/samples/GettingStarted/Agents/Agent_Step11_UsingImages/Program.cs

@@ -0,0 +1,30 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+// This sample shows how to use Image Multi-Modality with an AI agent.
+
+using System;
+using Azure.AI.OpenAI;
+using Azure.Identity;
+using Microsoft.Extensions.AI;
+using OpenAI;
+
+var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
+var deploymentName = System.Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o";
+
+var agent = new AzureOpenAIClient(new Uri(endpoint), new AzureCliCredential())
+    .GetChatClient(deploymentName)
+    .CreateAIAgent(
+        name: "VisionAgent",
+        instructions: "You are a helpful agent that can analyze images");
+
+ChatMessage message = new(ChatRole.User, [
+    new TextContent("What do you see in this image?"),
+    new UriContent("https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg", "image/jpeg")
+]);
+
+var thread = agent.GetNewThread();
+
+await foreach (var update in agent.RunStreamingAsync(message, thread))
+{
+    Console.WriteLine(update);
+}