### Description
The replay gain preferences are applied in the legacy code, but the
playout code was missing this feature. The replay gain was not applied
when playout fetched the schedules.
37d1a7685e/legacy/application/models/Schedule.php (L881-L886)
BREAKING CHANGE: The `general.secret_key` configuration field is now
required. Make sure to update your configuration file and add a secret
key.
Closes#2426
Jonas L
jo