Add a default value for do_refer in Dialog (#2383)

### What problem does this PR solve?

Add a default value for do_refer in Dialog

### Type of change

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

---------

Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

api/db/db_models.py

@@ -830,6 +830,7 @@ class Dialog(DataBaseModel):
     do_refer = CharField(
         max_length=1,
         null=False,
+        default="1",
         help_text="it needs to insert reference index into answer or not")
     
     rerank_id = CharField(