Bug 7491: improve description of the item-level_itypes syspref

Bug 7491: improve description of the item-level_itypes syspref

Adding some text to the pref description referring to OPAC display.

Test plan:
Look at the new description in Cataloging preferences.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 5dcf1857dac7d4c4a75a4e630938b8462542bcf3)
Signed-off-by: Fridolin SOMERS <fridolin.somers@biblibre.com>
(cherry picked from commit 735b7ea1909c7f3cf45855fc54931d837459f20e)
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>