.Net: OpenAI V2 - Migrated FileService - Phase 05 (#7076)

### Motivation and Context

- Added FileService OpenAI V2 Implementation
- Updated Extensions and UT accordingly
- Updated ClientCore to be used with FileService and allow non-required
`modelId`.

dotnet/src/Connectors/Connectors.OpenAIV2.UnitTests/Core/ClientCoreTests.cs

@@ -222,15 +222,6 @@ public void ItAddOrNotOrganizationIdAttributeWhenProvided()
         Assert.False(clientCoreWithoutOrgId.Attributes.ContainsKey(ClientCore.OrganizationKey));
     }
 
-    [Fact]
-    public void ItThrowsIfModelIdIsNotProvided()
-    {
-        // Act & Assert
-        Assert.Throws<ArgumentException>(() => new ClientCore(" ", "apikey"));
-        Assert.Throws<ArgumentException>(() => new ClientCore("", "apikey"));
-        Assert.Throws<ArgumentNullException>(() => new ClientCore(null!));
-    }
-
     [Fact]
     public void ItThrowsWhenNotUsingCustomEndpointAndApiKeyIsNotProvided()
     {

dotnet/src/Connectors/Connectors.OpenAIV2.UnitTests/Extensions/KernelBuilderExtensionsTests.cs

@@ -2,6 +2,7 @@
 
 using Microsoft.SemanticKernel;
 using Microsoft.SemanticKernel.AudioToText;
+using Microsoft.SemanticKernel.Connectors.OpenAI;
 using Microsoft.SemanticKernel.Embeddings;
 using Microsoft.SemanticKernel.Services;
 using Microsoft.SemanticKernel.TextToAudio;
@@ -132,4 +133,15 @@ public void ItCanAddAudioToTextServiceWithOpenAIClient()
         // Assert
         Assert.Equal("model", service.Attributes[AIServiceExtensions.ModelIdKey]);
     }
+
+    [Fact]
+    public void ItCanAddFileService()
+    {
+        // Arrange
+        var sut = Kernel.CreateBuilder();
+
+        // Act
+        var service = sut.AddOpenAIFiles("key").Build()
+            .GetRequiredService<OpenAIFileService>();
+    }
 }

dotnet/src/Connectors/Connectors.OpenAIV2.UnitTests/Extensions/OpenAIFileUploadExecutionSettingsTests.cs

@@ -0,0 +1,24 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using Microsoft.SemanticKernel.Connectors.OpenAI;
+using Xunit;
+
+namespace SemanticKernel.Connectors.OpenAI.UnitTests.Extensions;
+
+public class OpenAIFileUploadExecutionSettingsTests
+{
+    [Fact]
+    public void ItCanCreateOpenAIFileUploadExecutionSettings()
+    {
+        // Arrange
+        var fileName = "file.txt";
+        var purpose = OpenAIFilePurpose.FineTune;
+
+        // Act
+        var settings = new OpenAIFileUploadExecutionSettings(fileName, purpose);
+
+        // Assert
+        Assert.Equal(fileName, settings.FileName);
+        Assert.Equal(purpose, settings.Purpose);
+    }
+}

dotnet/src/Connectors/Connectors.OpenAIV2.UnitTests/Extensions/ServiceCollectionExtensionsTests.cs

@@ -3,6 +3,7 @@
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.SemanticKernel;
 using Microsoft.SemanticKernel.AudioToText;
+using Microsoft.SemanticKernel.Connectors.OpenAI;
 using Microsoft.SemanticKernel.Embeddings;
 using Microsoft.SemanticKernel.Services;
 using Microsoft.SemanticKernel.TextToAudio;
@@ -133,4 +134,16 @@ public void ItCanAddAudioToTextServiceWithOpenAIClient()
         // Assert
         Assert.Equal("model", service.Attributes[AIServiceExtensions.ModelIdKey]);
     }
+
+    [Fact]
+    public void ItCanAddFileService()
+    {
+        // Arrange
+        var sut = new ServiceCollection();
+
+        // Act
+        var service = sut.AddOpenAIFiles("key")
+            .BuildServiceProvider()
+            .GetRequiredService<OpenAIFileService>();
+    }
 }

dotnet/src/Connectors/Connectors.OpenAIV2.UnitTests/Services/OpenAIAudioToTextServiceTests.cs

@@ -45,6 +45,18 @@ public void ConstructorWithApiKeyWorksCorrectly(bool includeLoggerFactory)
         Assert.Equal("model-id", service.Attributes["ModelId"]);
     }
 
+    [Fact]
+    public void ItThrowsIfModelIdIsNotProvided()
+    {
+        // Act & Assert
+        Assert.Throws<ArgumentException>(() => new OpenAIAudioToTextService(" ", "apikey"));
+        Assert.Throws<ArgumentException>(() => new OpenAIAudioToTextService(" ", openAIClient: new("apikey")));
+        Assert.Throws<ArgumentException>(() => new OpenAIAudioToTextService("", "apikey"));
+        Assert.Throws<ArgumentException>(() => new OpenAIAudioToTextService("", openAIClient: new("apikey")));
+        Assert.Throws<ArgumentNullException>(() => new OpenAIAudioToTextService(null!, "apikey"));
+        Assert.Throws<ArgumentNullException>(() => new OpenAIAudioToTextService(null!, openAIClient: new("apikey")));
+    }
+
     [Theory]
     [InlineData(true)]
     [InlineData(false)]