Suppress alerts for legitimate certificates found on local system

[AGWA]

For example, in the certbot state directory (inspired by https://mas.to/@zekjur/111273573539477069)

[chayleaf]

It would be convenient to either provide the certificates directory to the program to verify certs against, or at least simply create an option for running a script that returns 0 if a certificate update should be notified about and 1 if it shouldn't