Bug 16755 - allow SIP2 field DA ( hold patron name ) to be customized

Bug 16755 - allow SIP2 field DA ( hold patron name ) to be customized

The SIP2 DA field that Koha transmits is an odd and arbitrary format
that some SIP2 clients cannot handle. It would be best if this
format were customizable on a per-login basis in the same manner as
the AV field.

Test Plan:
1) Find an item that is checked out with holds
2) Return the item via SIP2 ( using the SIP2 cli emulator )
3) Note the value of the DA field
4) Apply this patch, restart your SIP2 server
5) Repeat step 2
6) Note the DA field value has not changed
7) Add this parameter to the login stanza you are using:
   da_field_template="[% patron.surname %][% IF patron.firstname %], [% patron.firstname %][% END %]"
8) Restart the SIP2 server again
9) Repeat step 2
10) Note the DA field returned is now in the format "$surname, $firstname"

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Benjamin Daeuber <BDaeuber@cityoffargo.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>