sysutils/nut*: Use a dedicated UID and GID

To reduce conflicts with other packages and improve security, avoid
using the uucp UID and GID. This avoids potential conflicts with the
net/freebsd-uucp port.

Users who wish to continue using the uucp user and group may add
NUT_USER=uucp and NUT_GROUP=uucp to their make.conf.

PR: 268960
Reported by: delphij
MFH: 2023Q1