Bug 34885: Improve confusing pref description for OPACHoldsIfAvailableAtPickup

Bug 34885: Improve confusing pref description for OPACHoldsIfAvailableAtPickup

Changes pref description and sysprefs.sql.
The change is not important enough for a dbrev.

Test plan:
Look at the changed text in Systempreferences.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 1a398c5e9dab3a31d827ab7980899e0366353a37)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>