.Net: Add Ollama ChatCompletion with Vision Sample (#11113)

### Motivation and Context

Add missing sample using Ollama with Vision capable local model
`llama3.2-vision`.

- Fixes a small bug where using the `AddOllamaChatCompletion("modelId")`
throws an exception because no `BaseAddress` is provided in the
`httpClient` when it's null.

Author: RogerBarreto

Diff for: dotnet/samples/Concepts/ChatCompletion/Ollama_ChatCompletionWithVision.cs

@@ -0,0 +1,43 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using Microsoft.SemanticKernel;
+using Microsoft.SemanticKernel.ChatCompletion;
+using Resources;
+
+namespace ChatCompletion;
+
+/// <summary>
+/// This sample shows how to use llama3.2-vision model with different content types (text and image).
+/// </summary>
+public class Ollama_ChatCompletionWithVision(ITestOutputHelper output) : BaseTest(output)
+{
+    /// <summary>
+    /// This sample uses a local image file and sends it to the model along
+    /// with a text message the get the description of the image.
+    /// </summary>
+    [Fact]
+    public async Task GetLocalImageDescription()
+    {
+        Console.WriteLine($"======== Ollama - {nameof(GetLocalImageDescription)} ========");
+
+        var imageBytes = await EmbeddedResource.ReadAllAsync("sample_image.jpg");
+
+        var kernel = Kernel.CreateBuilder()
+            .AddOllamaChatCompletion(modelId: "llama3.2-vision", endpoint: new Uri(TestConfiguration.Ollama.Endpoint))
+            .Build();
+
+        var chatCompletionService = kernel.GetRequiredService<IChatCompletionService>();
+
+        var chatHistory = new ChatHistory("You are a friendly assistant.");
+
+        chatHistory.AddUserMessage(
+        [
+            new TextContent("What’s in this image?"),
+            new ImageContent(imageBytes, "image/jpg")
+        ]);
+
+        var reply = await chatCompletionService.GetChatMessageContentAsync(chatHistory);
+
+        Console.WriteLine(reply.Content);
+    }
+}

Diff for: dotnet/samples/Concepts/README.md

@@ -72,6 +72,7 @@ dotnet test -l "console;verbosity=detailed" --filter "FullyQualifiedName=ChatCom
 - [MultipleProviders_ChatHistoryReducer](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/ChatCompletion/MultipleProviders_ChatHistoryReducer.cs)
 - [Ollama_ChatCompletion](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/ChatCompletion/Ollama_ChatCompletion.cs)
 - [Ollama_ChatCompletionStreaming](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/ChatCompletion/Ollama_ChatCompletionStreaming.cs)
+- [Ollama_ChatCompletionWithVision](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/ChatCompletion/Ollama_ChatCompletionWithVision.cs)
 - [Onnx_ChatCompletion](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/ChatCompletion/Onnx_ChatCompletion.cs)
 - [Onnx_ChatCompletionStreaming](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/ChatCompletion/Onnx_ChatCompletionStreaming.cs)
 - [OpenAI_ChatCompletion](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/ChatCompletion/OpenAI_ChatCompletion.cs)