add expiry_date to task model

app/db.py

@@ -20,6 +20,7 @@ class Task(db.Model):
     is_completed = db.Column(db.Boolean)
     created_timestamp = db.Column(db.Integer)
     due_timestamp = db.Column(db.Integer)
+    expiry_date = db.Column(db.String(100))
 
     def __repr__(self):
         return f'<Task "{self.title}">'