Use finetune_right_pad_id token if available in KFTO SFT example

Author: astefanutti

examples/kfto-sft-llm/sft.ipynb

@@ -198,7 +198,12 @@
     "        model_args.model_name_or_path, trust_remote_code=model_args.trust_remote_code, use_fast=True\n",
     "    )\n",
     "    if tokenizer.pad_token is None:\n",
-    "        tokenizer.pad_token = tokenizer.eos_token\n",
+    "        # Models like Llama 3 use a dedicated padding token\n",
+    "        right_pad_id = tokenizer.convert_tokens_to_ids('<|finetune_right_pad_id|>')\n",
+    "        if right_pad_id is not None:\n",
+    "            tokenizer.pad_token = '<|finetune_right_pad_id|>'\n",
+    "        else:\n",
+    "            tokenizer.pad_token = tokenizer.eos_token\n",
     "\n",
     "    # Chat template\n",
     "    # You may need to provide your own chat template if the model does not have a default one\n",