Variables in Nginx configuration (#853)

* Add envsubst binary to image

* Generate nginx.conf from template, with env-vars

* Remove nginx.conf, now generated from template

* Reload nginx config after writing file

Co-authored-by: Shane Kilkelly <shane.kilkelly@overleaf.com>

server-ce/Dockerfile-base

@@ -30,6 +30,11 @@ RUN apt-get update \
       /etc/nginx/sites-enabled/default \
       /var/lib/apt/lists/*
 
+# Add envsubst
+# ------------
+ADD ./vendor/envsubst /usr/bin/envsubst
+RUN chmod +x /usr/bin/envsubst
+
 # Install Grunt
 # ------------
 RUN npm install -g \