Feature request: please add --test to report on config errors

[wellloaded]

dnsmasq comes with a built in "--test" function that easily reports on issues with configuration directives.
This apparently secondary function is instead vital on systems like routers where users are allowed (even remotely) to modify the DNS configuration config.

In this sense, it would be amazing to get a "--test" (usable with the existing -C) function available for stubby so that a custom .yalm could be checked and an exit code returned. This could prevent service downtime/interruptions and especially automatic system recovery, e.g. bypassing custom .yalm and sticking to the default if ever needed.

Thanks