Update conf.pp

Added an option to allow you to determine the name of the file in the sudoers.d folder yourself, instead of automatic naming. I was having issues where the sudoers file created by foreman (called ```foreman-proxy```) was deleted since I had purge enabled.

I would like to keep purge enabled, but I need to foreman-proxy file to remain (obviously) or I wont be able to manage my puppet certificates from within foreman.