The `ConditionFileIsExecutable` goes in the [Unit] section! This
fixes the error:
systemd[1]: [/etc/systemd/system/renew-letsencrypt.service:6] Unknown lvalue 'ConditionFileIsExecutable' in section 'Service'
Take an opinionated stance on HTTPS and assume that hosts are using
HTTPS for all vhosts. This can either be via custom TLS cert/key
pairs defined in the host's variables (could even be self-signed
certificates on dev boxes) or via Let's Encrypt.