.Net: Example of retry logic using Filters (#6152)

### Motivation and Context

<!-- Thank you for your contribution to the semantic-kernel repo!
Please help reviewers and future users, providing the following
information:
  1. Why is this change required?
  2. What problem does it solve?
  3. What scenario does it contribute to?
  4. If it fixes an open issue, please link to the issue here.
-->

Based on: #6105

This example shows how to perform retry with filter and switch to
another model as a fallback.

### Contribution Checklist

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

- [x] The code builds clean without any errors or warnings
- [x] 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
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

dotnet/samples/Concepts/Filtering/RetryWithFilters.cs

@@ -0,0 +1,72 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Net;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.SemanticKernel;
+using Microsoft.SemanticKernel.Connectors.OpenAI;
+
+namespace Filtering;
+
+/// <summary>
+/// This example shows how to perform retry with filter and switch to another model as a fallback.
+/// </summary>
+public class RetryWithFilters(ITestOutputHelper output) : BaseTest(output)
+{
+    [Fact]
+    public async Task ChangeModelAndRetryAsync()
+    {
+        // Default and fallback models for demonstration purposes
+        const string DefaultModelId = "gpt-4";
+        const string FallbackModelId = "gpt-3.5-turbo-1106";
+
+        var builder = Kernel.CreateBuilder();
+
+        // Add OpenAI chat completion service with invalid API key to force a 401 Unauthorized response
+        builder.AddOpenAIChatCompletion(modelId: DefaultModelId, apiKey: "invalid_key");
+
+        // Add OpenAI chat completion service with valid configuration as a fallback
+        builder.AddOpenAIChatCompletion(modelId: FallbackModelId, apiKey: TestConfiguration.OpenAI.ApiKey);
+
+        // Add retry filter
+        builder.Services.AddSingleton<IFunctionInvocationFilter>(new RetryFilter(FallbackModelId));
+
+        // Build kernel
+        var kernel = builder.Build();
+
+        // Initially, use "gpt-4" with invalid API key to simulate exception
+        var executionSettings = new OpenAIPromptExecutionSettings { ModelId = DefaultModelId, MaxTokens = 20 };
+
+        var result = await kernel.InvokePromptAsync("Hi, can you help me today?", new(executionSettings));
+
+        Console.WriteLine(result);
+
+        // Output: Of course! I'll do my best to help you. What do you need assistance with?
+    }
+
+    /// <summary>
+    /// Filter to change the model and perform retry in case of exception.
+    /// </summary>
+    private sealed class RetryFilter(string fallbackModelId) : IFunctionInvocationFilter
+    {
+        public async Task OnFunctionInvocationAsync(FunctionInvocationContext context, Func<FunctionInvocationContext, Task> next)
+        {
+            try
+            {
+                // Try to invoke function
+                await next(context);
+            }
+            // Catch specific exception
+            catch (HttpOperationException exception) when (exception.StatusCode == HttpStatusCode.Unauthorized)
+            {
+                // Get current execution settings
+                PromptExecutionSettings executionSettings = context.Arguments.ExecutionSettings![PromptExecutionSettings.DefaultServiceId];
+
+                // Override settings with fallback model id
+                executionSettings.ModelId = fallbackModelId;
+
+                // Try to invoke function again
+                await next(context);
+            }
+        }
+    }
+}

dotnet/samples/Concepts/README.md

@@ -59,6 +59,7 @@ Down below you can find the code snippets that demonstrate the usage of many Sem
 - [FunctionInvocationFiltering](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Filtering/FunctionInvocationFiltering.cs)
 - [Legacy_KernelHooks](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Filtering/Legacy_KernelHooks.cs)
 - [PromptRenderFiltering](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Filtering/PromptRenderFiltering.cs)
+- [RetryWithFilters](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Filtering/RetryWithFilters.cs)
 
 ## Functions - Invoking [`Method`](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/src/SemanticKernel.Core/Functions/KernelFunctionFromMethod.cs) or [`Prompt`](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/src/SemanticKernel.Core/Functions/KernelFunctionFromPrompt.cs) functions with [`Kernel`](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/src/SemanticKernel.Abstractions/Kernel.cs)