Previously, streams used `notifications`. Now they have separate
`desktop_notifications` and `audible_notifications`.
On staging, this should be run after the schema migration has been
applied (and technically before the code that uses the new fields is
deployed, but for staging, processing our notification settings a few
minutes late won't hurt anyone).
On prod, the script should be re-run just before the code using the
new notification settings is deployed to process any customer
notification settings changed since the staging deploy.
(imported from commit d99d238cd1b317c5180d7f940d70a7e2f8f9c712)
Jessica McKellar