Add chat template

See https://learn.microsoft.com/en-us/azure/ai-services/openai/how-to/chatgpt?tabs=python&pivots=programming-language-chat-ml for more information.

tokenizer_config.json

@@ -5,5 +5,6 @@
   "eos_token": "<|endoftext|>",
   "model_max_length": 8192,
   "tokenizer_class": "GPT4Tokenizer",
-  "unk_token": "<|endoftext|>"
+  "unk_token": "<|endoftext|>",
+  "chat_template": "{% for message in messages %}{{'<|im_start|>' + message['role'] + '\n' + message['content'] + '<|im_end|>' + '\n'}}{% endfor %}{% if add_generation_prompt %}{{ '<|im_start|>assistant\n' }}{% endif %}"
 }