.Net: Add a Unit Test to ensure the Service Attributes defined previously in the service are available in the ServiceSelector to be used as a filter. (#4854)

### Motivation and Context

Closes #3465 

### 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 😄

dotnet/src/SemanticKernel.UnitTests/Functions/CustomAIServiceSelectorTests.cs

@@ -0,0 +1,64 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Collections.Generic;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.SemanticKernel;
+using Microsoft.SemanticKernel.Services;
+using Xunit;
+
+namespace SemanticKernel.UnitTests.Functions;
+
+public class CustomAIServiceSelectorTests
+{
+    [Fact]
+    public void ItGetsAIServiceUsingArbitraryAttributes()
+    {
+        // Arrange
+        IKernelBuilder builder = Kernel.CreateBuilder();
+        builder.Services.AddKeyedSingleton<IAIService>("service1", new AIService());
+        Kernel kernel = builder.Build();
+
+        var function = kernel.CreateFunctionFromPrompt("Hello AI");
+        var serviceSelector = new CustomAIServiceSelector();
+
+        // Act
+        (var aiService, var defaultExecutionSettings) = serviceSelector.SelectAIService<IAIService>(kernel, function, new KernelArguments());
+
+        // Assert
+        Assert.NotNull(aiService);
+        Assert.True(aiService.Attributes?.ContainsKey("Key1"));
+        Assert.Null(defaultExecutionSettings);
+    }
+
+    private sealed class CustomAIServiceSelector : IAIServiceSelector
+    {
+#pragma warning disable CS8769 // Nullability of reference types in value doesn't match target type. Cannot use [NotNullWhen] because of access to internals from abstractions.
+        bool IAIServiceSelector.TrySelectAIService<T>(Kernel kernel, KernelFunction function, KernelArguments arguments, out T? service, out PromptExecutionSettings? serviceSettings) where T : class
+        {
+            var keyedService = (kernel.Services as IKeyedServiceProvider)?.GetKeyedService<T>("service1");
+            if (keyedService is null || keyedService.Attributes is null)
+            {
+                service = null;
+                serviceSettings = null;
+                return false;
+            }
+
+            service = keyedService.Attributes.ContainsKey("Key1") ? keyedService as T : null;
+            serviceSettings = null;
+            return true;
+        }
+    }
+
+    private sealed class AIService : IAIService
+    {
+        public IReadOnlyDictionary<string, object?> Attributes => this._attributes;
+
+        public AIService()
+        {
+            this._attributes = new Dictionary<string, object?>();
+            this._attributes.Add("Key1", "Value1");
+        }
+
+        private readonly Dictionary<string, object?> _attributes;
+    }
+}