Bug 28393: Elasticsearch - Add 050a to lc-call-number index mapping (MARC21)

Bug 28393: Elasticsearch - Add 050a to lc-call-number index mapping (MARC21)

This patch adds 050 $a to the mapping for the lc-call-number index.

To test:
1) Apply patch
2) Reindex using rebuild_elasticsearch.pl -r

If you don't have access to a terminal (in a sandbox for example)
2a) Go to Administration > Search engine configuration, click "Reset mappings"
and confirm
2b) Then reindex

I'm not sure how to search specifically for an LC call number.
You can confirm that 050 $a is displayed in the Search engine configuration page.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>