Feature/caddy frontend slave log on real frontend

TODOs:

• reload nginx on changes of the config
• request frontend on each frontend node
• use the requested frontend while exposing access to logs
• cover with tests
• remove etc/caddy-slave-conf.d/.<REFERENCE>.passwd if not needed
  • it's a storage of password generator, so no removal happened
• setup proper mime type from nginx_mime
• logrotate support