net-mgmt/nrpe: Adding monplugins flavor to nrpe
Some user asked to add a flavor to permit to have nrpe already
packaged with monplugins.
This patch add this functionality and has been tested (both
flavors default and monplugins with poudriere under 13.4-RELEASE).
Sponsored by: Klara, Inc.
Approved by: 0mp (mentor)
Approved by: bofh (maintainer)
Differential Revision: https://reviews.freebsd.org/D48111