Bug 28379: Elasticsearch - Add 710 to author-name-corporate index (MARC21)

Bug 28379: Elasticsearch - Add 710 to author-name-corporate index (MARC21)

This patch adds 710 to the default author-name-corporate index mappings for
elasticsearch.

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

3) Search for an author name found only in 710 using the Author (Corporate name) index
in advanced search

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>