c5200e8b05 switched `digest_emails` from sending emails by inserting
into the ScheduledEmail table, and being processed later by
`deliver_scheduled_emails`, to inserting into the
`deferred_email_senders` RabbitMQ queue. This moved it from being in
an unmonitored table, to a monitored queue.
This slightly improved throughput -- but began paging, since the
backlog was now in a monitored form. Increase the paging thresholds
to not page for expected behaviour.
232de4b98f