update text-to-sql cookbook

cookbook/pocketflow-text2sql/utils/call_llm.py

@@ -0,0 +1,14 @@
+import os
+from openai import OpenAI
+
+def call_llm(prompt):    
+    client = OpenAI(api_key=os.environ.get("OPENAI_API_KEY", "your-api-key"))
+    r = client.chat.completions.create(
+        model="gpt-4o",
+        messages=[{"role": "user", "content": prompt}]
+    )
+    return r.choices[0].message.content
+
+# Example usage
+if __name__ == "__main__":
+    print(call_llm("Tell me a short joke"))