Bug 33563: Add comments for Elasticsearch security config

Bug 33563: Add comments for Elasticsearch security config

This patch adds some commented Elasticsearch security configuration,
which shows how to use username/password with HTTPS.

Test plan:
0. Apply patch
1. cp debian/templates/koha-conf-site.xml.in /etc/koha/koha-conf-site.xml.in
2. koha-create --create-db test
3. vi /etc/koha/sites/test/koha-conf.xml
4. Note that the comments for userinfo and use_https are in the koha-conf.xml

Signed-off-by: Magnus Enger <magnus@libriotech.no>
Works as advertised.
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>