This changes log2ram dependencies to start as early as possible, before other
services that may require access to /var/log, including rsyslog and
systemd-journald.
Additional dependencies on shutdown.target are required to ensure that
the service will be stopped at shutdown/reboot when DefaultDependencies
is set to "no" [1].
RequiresMountsFor declares dependency on /var mount when it is a mount point.
IgnoreOnIsolate prevents stopping the service when isolating another unit.
[1]: https://www.freedesktop.org/software/systemd/man/systemd.service.html
From @datenklause
With Type=oneshot, systemd waits until the start action has completed
before it considers the unit to be active, so dependencies start only
after the start action has succeeded. With Type=simple, dependencies
will start immediately after the start action has been dispatched.
