certbot should exit non-zero if any deploy hook failed

This is a request raised on the forum.

If Certbot fails to deploy a certificate (to a remote server for example), then, in the big picture, the renewal did not really succeed.

In that case, the lack of success should be reflected in a non-zero exit code. This would allow other tools to pick up on the failure, e.g. if you have something monitoring the status of systemd units.

Tangentially related is this Certbot user experience: https://utcc.utoronto.ca/~cks/space/blog/linux/SystemdTimersAndErrors. "Cron will email the user any errors" is an outdated mindset, should that be reflected by the project in any way?