search: drop_old_data: refactor to util.drop_older_than method.
This MR is a proposal to refactor data retention tasks to use the wmf_airflow_common
drop_older_than helper method.
Context
!940 (merged) introduced a new drop_older_than
utility method that wraps refinery's drop-older-than script for data retention.
Data retention, and execution of python scripts, for the drop_old_data could now be expressed using wmf_airflow_common APIs instead of an
ad-hoc implementation.
Note however that the API is tagged as experimental because of an RFC (pending review) that propose to generalize data retention config via the DatasetRegistry API.
cc / @dcausse @ebernhardson