set ollama keep_alive (#985)

### What problem does this PR solve?

#980 

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/db/init_data.py

         {
             "fid": factory_infos[12]["name"],
             "llm_name": "BAAI/bge-reranker-v2-m3",
-            "tags": "LLM,CHAT,",
-            "max_tokens": 16385,
+            "tags": "RE-RANK,2k",
+            "max_tokens": 2048,
             "model_type": LLMType.RERANK.value
         },
     ]

rag/llm/chat_model.py

             response = self.client.chat(
                 model=self.model_name,
                 messages=history,
-                options=options
+                options=options,
+                keep_alive=-1
             )
             ans = response["message"]["content"].strip()
             return ans, response["eval_count"] + response.get("prompt_eval_count", 0)
                 model=self.model_name,
                 messages=history,
                 stream=True,
-                options=options
+                options=options,
+                keep_alive=-1
             )
             for resp in response:
                 if resp["done"]: