fix: model type only support single value (#1884)

### What problem does this PR solve?

 model type only support single value
### Type of change

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

Co-authored-by: Zhedong Cen <cenzhedong2@126.com>

conf/llm_factories.json

                     "llm_name": "gpt-4o-mini",
                     "tags": "LLM,CHAT,128K",
                     "max_tokens": 128000,
-                    "model_type": "image2text"
+                    "model_type": "chat"
                 },
                 {
                     "llm_name": "gpt-4o",
                     "tags": "LLM,CHAT,128K",
                     "max_tokens": 128000,
-                    "model_type": "chat,image2text"
+                    "model_type": "chat"
                 },
                 {
                     "llm_name": "gpt-3.5-turbo",