You could do this as part of the backup of configs job. I get an email once a week that shows me the difference (I only back up configs once a week). Basically I have 1 job that does all the startup configs. Then I have a second job that starts 1 hour later and it backs up all the running configs. And as part of that job I've ticked "Send a notification if the downloaded Config is different than the - Startup Config" As per image below.
