some model name changing, and constains model improvement

app/models/constraint.py

@@ -1,10 +1,9 @@
 from pydantic import BaseModel
 from typing import Optional
 
+from models.attribute import Attribute
+
 class Constraint(BaseModel):
-  key: str
-  value: str
-  field_id: Optional[int]
-  option_id: Optional[int]
+  reference_attribute: Attribute
   minimum: int
   maximum: int