Shorten security_event_logs time horizon to match event_logs

Created by: flying-robot

We have an order of magnitude more security_event_log rows than normal event_log rows. Since the table is intended for consumption by data pipelines vs. direct queries, it makes sense to shorten the time horizon and free up database resources accordingly.

This drops that horizon from 6 months to 1 week, which will help keep the table and indices at a manageable level.