Fix memory extraction json format issue (#1193)

### Motivation and Context

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Model hasn't been generating JSON consistently for memory extraction. 

### Description

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Set the response format to JSON to force the model to output valid json
for memory extraction.


### Contribution Checklist

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- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [Contribution
Guidelines](https://github.com/microsoft/chat-copilot/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/chat-copilot/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 😄

webapi/Controllers/ChatMemoryController.cs

@@ -97,7 +97,7 @@ await memoryClient.SearchMemoryAsync(
                     this._promptOptions.MemoryIndexName,
                     "*",
                     relevanceThreshold: 0,
-                    resultCount: 1,
+                    resultCount: -1,
                     chatId,
                     memoryContainerName);
 

webapi/Plugins/Chat/SemanticChatMemoryExtractor.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System;
+using System.Collections.Generic;
 using System.Globalization;
 using System.Threading;
 using System.Threading.Tasks;
@@ -11,6 +12,7 @@
 using Microsoft.Extensions.Logging;
 using Microsoft.KernelMemory;
 using Microsoft.SemanticKernel;
+using Microsoft.SemanticKernel.Connectors.OpenAI;
 
 namespace CopilotChat.WebApi.Plugins.Chat;
 
@@ -78,7 +80,13 @@ async Task<SemanticChatMemory> ExtractCognitiveMemoryAsync(string memoryType, st
                 options.ResponseTokenLimit -
                 TokenUtils.TokenCount(memoryPrompt);
 
-            var memoryExtractionArguments = new KernelArguments(kernelArguments);
+#pragma warning disable SKEXP0010 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
+            var memoryExtractionArguments = new KernelArguments(kernelArguments, executionSettings: new Dictionary<string, PromptExecutionSettings>
+            {
+                { PromptExecutionSettings.DefaultServiceId, new OpenAIPromptExecutionSettings { ResponseFormat = "json_object" } }
+            });
+#pragma warning restore SKEXP0010 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
+
             memoryExtractionArguments["tokenLimit"] = remainingToken.ToString(new NumberFormatInfo());
             memoryExtractionArguments["memoryName"] = memoryName;
             memoryExtractionArguments["format"] = options.MemoryFormat;