Ask systemd to delay the restart of the services by 5 seconds

This way we avoid too many restarts in a short time span which would make systemd stop restarting the service.

For most services this change is already deployed since a few months and I'm not aware of services (running on Linux) that died (were killed by systemd) when the SFTP server or GitLab was restarted. This means we can probably close !39 (closed) because the more intrusive changes in !39 (closed) aren't really needed.