Refactor (#537)

### What problem does this PR solve?

### Type of change

- [x] Refactoring

api/db/db_models.py

@@ -697,7 +697,7 @@ class Dialog(DataBaseModel):
         null=True,
         default="Chinese",
         help_text="English|Chinese")
-    llm_id = CharField(max_length=32, null=False, help_text="default llm ID")
+    llm_id = CharField(max_length=128, null=False, help_text="default llm ID")
     llm_setting = JSONField(null=False, default={"temperature": 0.1, "top_p": 0.3, "frequency_penalty": 0.7,
                                                  "presence_penalty": 0.4, "max_tokens": 215})
     prompt_type = CharField(