Automatic / programmatic config sync to backup (secondary)

[cloudguy]

Hello.   Would like to understand how to programmatically "Synchronize config to backup".   Our use case is:

* Two opnsense firewalls
* lets encrypt running on the one designated as "primary"
* upon trust change (new certs) would like to propagate to backup node
* I'm able to do this via "configctl filter sync restart" and cron, however would like to understand how this could work natively within opnsense system cron / api / etc.

Thanks.