Add additional nginx configuration

[galethil]

• The feature was discussed in discussions of this repository.
• I have searched the issues of this repository and believe that this is not a duplicate.

Description 💡

With some deployments additional configuration is required. Add "wildcard" variables for each servise that will allow to inject additional configuration to nginx server for each service.

if [ "$REACT_APP_EXPORT_SERVICE_ENABLED" = true ]; then
  echo "Excel export has been enabled"
  echo "$export_protocol://$export_host:$export_port/"
  sed -i -e "/# pathToExcelExport/i\\
  proxy_pass $export_protocol://$export_host:$export_port/;" /etc/nginx/conf.d/default.conf
fi

change with something similar to

if [ "$REACT_APP_EXPORT_SERVICE_ENABLED" = true ]; then
  echo "Excel export has been enabled"
  echo "$export_protocol://$export_host:$export_port/"
  sed -i -e "/# pathToExcelExport/i\\
  $additional_export_headers  # <<<<======
  proxy_pass $export_protocol://$export_host:$export_port/;" /etc/nginx/conf.d/default.conf
fi