Copy a file as a pkg.conf(5) file.
Instead of creating the /usr/local/etc/pkg/repos directory and placing a custom pkg.conf(5) file there over and over again for each Makejail, when this Makejail is included, it does so whenever the pkg_conf argument is set. If pkg_conf is set, the file is saved as /usr/local/etc/pkg/repos/${pkg_name}.conf, where the pkg_name argument defaults to FreeBSD.