Scheduled tasks to clean up the database

- tasks run hourly
- uses celery beat to schedule the tasks

4 new tasks
- delete verify codes (after 1 day)
- delete invitations (after 1 day)
- delete successful notifications  (after 1 day)
- delete failed notifications (after 7 days)

Delete methods in the DAO classes

app/dao/invited_user_dao.py

@@ -1,3 +1,4 @@
+from datetime import datetime, timedelta
 from app import db
 
 from app.models import InvitedUser
@@ -18,3 +19,11 @@ def get_invited_user_by_id(invited_user_id):
 
 def get_invited_users_for_service(service_id):
     return InvitedUser.query.filter_by(service_id=service_id).all()
+
+
+def delete_invitations_older_created_more_than_a_day_ago():
+    deleted = db.session.query(InvitedUser).filter(
+        InvitedUser.created_at <= datetime.utcnow() - timedelta(days=1)
+    ).delete()
+    db.session.commit()
+    return deleted