Bug 36134: Read complete Elasticsearch configuration in about.pl

Bug 36134: Read complete Elasticsearch configuration in about.pl

When enabling Elasticsearch authentication in Koha using userinfo
parameter of Search::Elasticsearch, about.pl breaks and gives an
internal server error.

This patch reads the complete Elasticsearch configuration for
about.pl including userinfo causing about.pl to recover.

To test:
1. In Elasticsearch 7 settings, set "xpack.security.enabled: true"
2. Add <userinfo>elastic:password</userinfo> to KOHA_CONF elasticsearch
   settings
3. Restart plack and navigate to about.pl
4. Observe internal server error
5. Apply patch
6. Refresh about.pl
7. Observe it working again

Signed-off-by: David Cook <dcook@prosentient.com.au>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>