Kubernetes migration: Fix end dates for webrequest DAGs in analytics folder

Last night we deployed some changes for the Airflow Kubernetes migration and we mistakenly set some end_dates for the webrequest DAGs in analytics that have not yet been migrated. The DAGs have stopped running as instructed, and hence the big amount of SLA alerts for the last 8 hours. This change sets the end_date of webrequest DAGs to a sensible value, to restore execution of those DAGs until we migrate them.

Bug: T386282