Configure DEFAULT_FROM_EMAIL
Refs https://redmine.teklia.com/issues/9742
To support a new transactional email service, we must be able to configure the DEFAULT_FROM_EMAIL setting to a specific value (other than email user).
You'll need to add a new optional setting email.from_address. When not set, the EMAIL_HOST_USER is used instead.
SERVER_EMAIL gets the same value as DEFAULT_FROM_EMAIL