.Net: Extend sample to show how to use MCP Tools from an Agent (#11361)

### Motivation and Context

Extend the sample to show how to use MCP Tools from an Agent.

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

---------

Co-authored-by: Roger Barreto <19890735+RogerBarreto@users.noreply.github.com>

Author: markwallace-microsoft

dotnet/samples/Demos/ModelContextProtocolPlugin/ModelContextProtocolPlugin.csproj

@@ -19,6 +19,8 @@
   </ItemGroup>
 
   <ItemGroup>
+    <ProjectReference Include="..\..\..\src\Agents\Abstractions\Agents.Abstractions.csproj" />
+    <ProjectReference Include="..\..\..\src\Agents\Core\Agents.Core.csproj" />
     <ProjectReference Include="..\..\..\src\Connectors\Connectors.AzureOpenAI\Connectors.AzureOpenAI.csproj" />
     <ProjectReference Include="..\..\..\src\SemanticKernel.Abstractions\SemanticKernel.Abstractions.csproj" />
     <ProjectReference Include="..\..\..\src\SemanticKernel.Core\SemanticKernel.Core.csproj" />

dotnet/samples/Demos/ModelContextProtocolPlugin/Program.cs

@@ -4,6 +4,7 @@
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
 using Microsoft.SemanticKernel;
+using Microsoft.SemanticKernel.Agents;
 using Microsoft.SemanticKernel.Connectors.OpenAI;
 using ModelContextProtocol;
 using ModelContextProtocol.Client;
@@ -70,3 +71,16 @@
 var prompt = "Summarize the last four commits to the microsoft/semantic-kernel repository?";
 var result = await kernel.InvokePromptAsync(prompt, new(executionSettings)).ConfigureAwait(false);
 Console.WriteLine($"\n\n{prompt}\n{result}");
+
+// Define the agent
+ChatCompletionAgent agent = new()
+{
+    Instructions = "Answer questions about GitHub repositories.",
+    Name = "GitHubAgent",
+    Kernel = kernel,
+    Arguments = new KernelArguments(new PromptExecutionSettings() { FunctionChoiceBehavior = FunctionChoiceBehavior.Auto() }),
+};
+
+// Respond to user input, invoking functions where appropriate.
+ChatMessageContent response = await agent.InvokeAsync("Summarize the last four commits to the microsoft/semantic-kernel repository?").FirstAsync();
+Console.WriteLine($"\n\nResponse from GitHubAgent:\n{response.Content}");