Retry renewal of SSL certificates

[jdno]

The renew-ssl-certs.service fails periodically, which triggers the following alert in Grafana:

The systemd unit renew-ssl-certs.service on the <server>:9100 instance failed to execute.

The fix for this alert is to restart the service manually:

sudo systemctl restart renew-ssl-certs.service

We should investigate the reason why the service fails in the first place and retry automatically.