feat: normally-off monitor

`note: self assign`
# feat: normally-off monitor
examples: validating firewalls, airgapping, etc.

the monitor is UP if the check fails and DOWN if the check passes. the checks (ping, http(s), port, etc) would remain the same.

Start by locating the existing monitor status handling and the implementations for ping, HTTP(S), and port checks. Trace how check success and failure become UP or DOWN, then determine where the normally-off setting must apply across those checks. Done means the inverted behavior is consistent and covered by the relevant tests, if present.

Written by the indexing model from the issue text.