Shortening plan object in chat history (#1306)

### Motivation and Context
Truncating plan object to intent only in chat history to save on token
limits.

![image](https://github.com/microsoft/semantic-kernel/assets/125500434/e8690c10-ac9e-4ae4-8506-6fd1426f1818)

Author: teresaqhoang

samples/apps/copilot-chat-app/webapi/CopilotChat/Skills/ChatSkills/ChatSkill.cs

@@ -5,6 +5,7 @@
 using System.Globalization;
 using System.Linq;
 using System.Text.Json;
+using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
@@ -156,10 +157,28 @@ public async Task<string> ExtractChatHistoryAsync(SKContext context)
         foreach (var chatMessage in sortedMessages)
         {
             var formattedMessage = chatMessage.ToFormattedString();
+
+            // Plan object is not meaningful content in generating bot response, so shorten to intent only to save on tokens
+            if (formattedMessage.Contains("proposedPlan\":", StringComparison.InvariantCultureIgnoreCase))
+            {
+                string pattern = @"(\[.*?\]).*User Intent:User intent: (.*)(?=""}})";
+                Match match = Regex.Match(formattedMessage, pattern);
+                if (match.Success)
+                {
+                    string timestamp = match.Groups[1].Value.Trim();
+                    string userIntent = match.Groups[2].Value.Trim();
+
+                    formattedMessage = $"{timestamp} Bot proposed plan to fulfill user intent: {userIntent}";
+                }
+                else
+                {
+                    formattedMessage = "Bot proposed plan";
+                }
+            }
+
             var tokenCount = Utilities.TokenCount(formattedMessage);
 
-            // Plan object is not meaningful content in generating chat response, exclude it
-            if (remainingToken - tokenCount > 0 && !formattedMessage.Contains("proposedPlan\\\":", StringComparison.InvariantCultureIgnoreCase))
+            if (remainingToken - tokenCount >= 0)
             {
                 historyText = $"{formattedMessage}\n{historyText}";
                 remainingToken -= tokenCount;