add a shell command to use the env variables

docker-compose.yml

@@ -10,6 +10,12 @@ services:
     environment:
       - MEDIA_API_KEY=key-mindboost-media-server # ⇦ beliebig ändern
       - SERVER_NAME=b.mindboost.team # ⇦ beliebig ändern
+    command: >
+      /bin/sh -c '
+        envsubst < /etc/nginx/conf.d/default.conf.template \
+                > /etc/nginx/conf.d/default.conf \
+        && nginx -t \
+        && exec nginx -g "daemon off;"'
     labels:
       - "traefik.enable=true"