Bug 18017: Add subdivisions to UNIMARC authorities zebra configuration

Bug 18017: Add subdivisions to UNIMARC authorities zebra configuration

Like for MARC21, UNIMARC authorities has subdivisions form, general,
chronological and geographic.

In C4::Heading::UNIMARC, use subdivisions in _get_search_heading like in C4::Heading::MARC21.

Adds subdivisions variables into UNIMARC authorities zebra configuration.

Note that unlike MARC21 geographic is subfield $y and chronological is subfield $z.
See https://www.ifla.org/publications/unimarc-formats-and-related-documentation

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>