sysutils/nut: Install nut-usb.conf

devd fails to change UPS device node ownership because the nut port
fails to install ${LOCALBASE}/etc/devd/nut-usb.conf. Install it.

Reported by: Kostas Oikonomou <ko56 _AT_ winlab.rutgers.edu>
MFH: 2023Q2

(cherry picked from commit 7267b89b748860bd8dbca6d8682ebb3a541892df)