net-mgmt/ping_exporter: Update to 1.2.0

Upstream release notes:
https://github.com/czerwonk/ping_exporter/releases/tag/v1.2.0

BREAKING CHANGE: The configuration file format has changed.
Refer to the above link for migration details.

Reviewed by: arrowd
Approved by: arrowd (ports)
Sponsored by: https://www.patreon.com/bsdivy
Differential Revision: https://reviews.freebsd.org/D56079