net-mgmt/bosun: create port

Bosun is an open-source, MIT licensed, monitoring and alerting system by
Stack Exchange.

It has an expressive domain specific language for evaluating alerts
and creating detailed notifications.
It also lets you test your alerts against history
for a faster development experience.

WWW: https://bosun.org/

PR: 250209
Submitted by: Markus Langer <langer.markus@gmail.com>