Bug 25873: Ignore malformed data for Elasticsearch integer fields

Bug 25873: Ignore malformed data for Elasticsearch integer fields

If we try to put malformed data into an integer field, Elasticsearch
rejects the whole document.
Setting 'ignore_malformed' to true allows to ignore malformed data and
process the other fields of the document normally

https://www.elastic.co/guide/en/elasticsearch/reference/7.8/ignore-malformed.html

Test plan:
* Without the patch
  1. In search engine configuration, change the type of a text field to
  'Number' (for instance 'title')
  2. misc/search_tools/rebuild_elasticsearch.pl -d -b
  3. See that the index is empty (unless you have titles consisting only
  of digits)
* With the patch
  1. misc/search_tools/rebuild_elasticsearch.pl -d -b
  2. Now records are correctly indexed

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>