Make it possible to add generic config blocks in sites and configs

Sometimes you have to deal with configuration blocks like:

http {
...
  upstream default {
    server 127.0.0.1:8080 weight=10;
    server 127.0.0.1:9090 weight=20;
    ...
  }
...
  server {
    ...
    if ( condition ) {
      ...
    }
    ...
    location / {
      ...
    }
    ...
  }
}

This commits make it possible to add such blocks to the /etc/nginx/conf.d/*.conf files generated by this role and to the /etc/nginx/sites-enabled/*.conf