Add environment variable to system service for custom settings

etc/systemd/system/metobs_api.service

@@ -9,6 +9,7 @@ User=daemon
 Group=metobsgrp
 RuntimeDirectory=metobs_api
 WorkingDirectory=/tmp
+Environment="METOBSAPI_SETTINGS=/home/metobs/metobs_api_settings.py"
 ExecStart=/opt/metobs/metobs_api/bin/gunicorn --pid /run/metobs_api/pid   \
           --bind unix:/run/metobs_api/socket --workers 8 -n metobs_api   \
           --max-requests 1000 metobsapi.server:app