Bug 30055: Put extended attributes search back

Bug 30055: Put extended attributes search back

Last patches remove the ability to search on extended attributes.
C4::Utils::DataTables::Members::search is searching on all the
attributes that are flagged as "searchable", we want to keep this
behaviour.

I have tried several things and this is the simplest I have found.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Séverine Queune <severine.queune@bulac.fr>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>