Bug 33404: Z3950SearchAuth: Save in UTF-8 encoding

Bug 33404: Z3950SearchAuth: Save in UTF-8 encoding

Test plan:
[1] If you have access to a Z3950 MARC8 auth server, search
    for an authority record and import it.
[2] If you have access to a Z3950 UTF8 auth server, search
    for an authority record and import it.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>