Set backend host header for frontend proxy

docker/docker-entrypoint.sh

@@ -2,11 +2,13 @@
 set -eu
 
 : "${BACKEND_UPSTREAM:?BACKEND_UPSTREAM is required (example: http://analytical-panel-backend:8000)}"
+: "${BACKEND_HOST_HEADER:?BACKEND_HOST_HEADER is required (example: analytical-panel-backend)}"
 
 BACKEND_UPSTREAM="${BACKEND_UPSTREAM%/}"
 export BACKEND_UPSTREAM
+export BACKEND_HOST_HEADER
 
-envsubst '${BACKEND_UPSTREAM}' \
+envsubst '${BACKEND_UPSTREAM} ${BACKEND_HOST_HEADER}' \
   < /etc/nginx/templates/default.conf.template \
   > /etc/nginx/conf.d/default.conf