Add back in SQLALCHEMY config changes on staging
Add back in SQLALCHEMY config changes on staging

SQL Alchemy config changes were made to decrease the downtime of the
application. The last test only had 1 min of downtime in the upgrade
period i.e. 40 mins. Tested without the config changes to double
check the change had the desired effect. Adding back in so we can test
the changes under load and performance test outside of upgrade.

alphagov/notifications-api,alphagov/notifications-api