Bug 36603: Copy the ISNI number over automatically

Bug 36603: Copy the ISNI number over automatically

When linking authorities with other authorities in UNIMARC
instances it would be good if Koha automatically copied the
contents of subfield 010$a [aka INTERNATIONAL STANDARD NAME
IDENTIFIER (ISNI)] into the corresponding 5xx$o subfield
(should such an ISNI number exist in the source record).

This patch enables the enhancement outlined above.

For more information, please see the offical IFLA UNIMARC
Authorities Format Manual (online ed., 1.0.0, 2023), pp. 350,
363, 385. This is actually where we got this idea from ;-)

Note #1: it only applies to the Personal Name, Corporate
         Body Name, and Family Name authority types.

Note #2: the default MARC Authorities framework that ships
         with UNIMARC Koha instances does *not* include a
         subfield $o for fields
         200 (Authorized Access Point - Personal Name),
         210 (Authorized Access Point - Corporate Body Name),
         220 (Authorized Access Point - Family Name).
         This is per the offical IFLA Manual, and effectively
         means we can push the ISNI number to the same array
         used for other subfields (@subfield_loop) without
         worrying about overwriting any previous value.

Test plan:

0) Have a UNIMARC Koha test instance up and running. Then,
   carry out the following steps in the Staff interface.

1) Stage for import the sample MARC authority data attached
   to this Bug report (filename: sample-auths.mrc, contains
   one Personal, one Corporate Body, and one Family Name).
   Go to 'Cataloging > Stage records for import' and upload
   the file. Make sure you select 'Authority' in the 'Record
   type' dropdown menu. Leave all other settings untouched at
   their default values. Click the 'Stage for import' button.

   Then, import the staged records into your Catalog. Go
   to 'Cataloging > Manage staged records'. Click on the
   filename link in the second column. At the bottom of the
   page, confirm you can see all three authorities included
   in the .mrc you uploaded, then click on the button named
   'Import this batch into the catalog'.

2) Enable the authority finder plugin for authority fields
   500, 510 and 520. This can be done as follows:

   a) Go to 'Administration > Authority types' and click on
      'Actions->MARC structure' for the 'NP' (Personal Name)
      authority type.
   b) Search for tag 500; then click on 'Actions->Subfields'
      for that tag.
   c) Click 'Edit' next to subfield 'a' (Entry element), then
      pick 'NP' from the 'Thesaurus' dropdown menu. Save your
      settings and you're good to go! When editing a Personal
      Name authority from now on, the 'Tag editor' button next
      to subfield 500$a will launch the authority finder.

   Repeat b) and c): search for tag 510, edit $a, pick 'CO'.
   Repeat b) and c): search for tag 520, edit $a, pick 'FAM'.

3) Go to Koha's 'Authorities' module. At the top search bar,
   filter on Personal Name authorities and perform a search.
   Pick any one of the results, and edit it. Go to tab '5',
   expand field 500 and use the button next to subfield $a
   to launch the authority finder. Type '0000' inside the
   'Search entire record:' text box, and click on 'Search',
   then 'Choose'.

   Notice that the ISNI number from the source record did
   *not* get copied to subfield 500$o. The same will happen
   if you try to Choose an authority for field 510 and 520.

4) Apply this patch.

5) Repeat step 3), this time the ISNI number from the source
   record will be copied to 500/510/520 $o automatically!

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>