Enable zfs-import.target in systemd preset

Cherry picked line from PR openzfs#6822, this enables the new
target introduced in PR openzfs#6764.

Signed-off-by: Antonio Russo <antonio.e.russo@gmail.com>

etc/systemd/system/50-zfs.preset.in

@@ -1,6 +1,7 @@
 # ZFS is enabled by default
 enable zfs-import-cache.service
 disable zfs-import-scan.service
+enable zfs-import.target
 enable zfs-mount.service
 enable zfs-share.service
 enable zfs-zed.service