Fix the deprecated load_model_by_config_name in the nl2sql example

examples/conversation_nl2sql/react_nl2sql.ipynb

@@ -46,12 +46,13 @@
    "source": [
     "from typing import Callable\n",
     "import agentscope\n",
-    "from agentscope.models import load_model_by_config_name\n",
     "agentscope.init(\n",
     "    model_configs=\"./configs/model_configs.json\",\n",
     "    project=\"Conversation with NL2SQL\",\n",
     ")\n",
-    "loaded_model = load_model_by_config_name('gpt-4')"
+    "from agentscope.manager import ModelManager\n",
+    "model_manager = ModelManager.get_instance()\n",
+    "loaded_model = model_manager.get_model_by_config_name('gpt-4')"
    ]
   },
   {