.Net Fix - Include role definition for each StreamingChatMessageContent (microsoft#6957)

### Motivation and Context
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`StreamingChatMessageContent.AuthorRole` always `null`

### Description
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Logic already exists to capture role, but it was not being passed to
each and every instance of StreamingChatMessageContent. Other
properties, such as `ModelId` are included with each and every instance.

Updated integration test.

Issue: microsoft#6952

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Author: crickman

dotnet/src/Connectors/Connectors.OpenAI/AzureSdk/ClientCore.cs

@@ -693,7 +693,18 @@ internal async IAsyncEnumerable<OpenAIStreamingChatMessageContent> GetStreamingC
                             OpenAIFunctionToolCall.TrackStreamingToolingUpdate(update.ToolCallUpdate, ref toolCallIdsByIndex, ref functionNamesByIndex, ref functionArgumentBuildersByIndex);
                         }
 
-                        var openAIStreamingChatMessageContent = new OpenAIStreamingChatMessageContent(update, update.ChoiceIndex ?? 0, this.DeploymentOrModelName, metadata) { AuthorName = streamedName };
+                        AuthorRole? role = null;
+                        if (streamedRole.HasValue)
+                        {
+                            role = new AuthorRole(streamedRole.Value.ToString());
+                        }
+
+                        OpenAIStreamingChatMessageContent openAIStreamingChatMessageContent =
+                            new(update, update.ChoiceIndex ?? 0, this.DeploymentOrModelName, metadata)
+                            {
+                                AuthorName = streamedName,
+                                Role = role,
+                            };
 
                         if (update.ToolCallUpdate is StreamingFunctionToolCallUpdate functionCallUpdate)
                         {

dotnet/src/IntegrationTests/Connectors/OpenAI/OpenAICompletionTests.cs

@@ -128,6 +128,11 @@ public async Task AzureOpenAIStreamingTestAsync(bool useChatModel, string prompt
         // Act
         await foreach (var content in target.InvokeStreamingAsync<StreamingKernelContent>(plugins["ChatPlugin"]["Chat"], new() { [InputParameterName] = prompt }))
         {
+            if (content is StreamingChatMessageContent messageContent)
+            {
+                Assert.NotNull(messageContent.Role);
+            }
+
             fullResult.Append(content);
         }