This file is used to set `USE_X_FORWARDED_HOST`, which is necessary to make Weblate work
correctly being an Apache (and potentially other HTTP servers) reverse proxy (otherwise we
have CSRF errors, cf. https://github.com/WeblateOrg/weblate/issues/1912).
when `email_from` was not set in `sat.conf`, no value was set for `WEBLATE_SERVER_EMAIL`
and `WEBLATE_DEFAULT_FROM_EMAIL`. These environment variables are needed for Weblate to be
launched, so default value are now used (the same as the one from official Weblate Docker
image).