Currently, if internal TLS communication is enabled, Kibana to
Elasticsearch communication is unverified. This is because we set
elasticsearch.ssl.verificationMode to 'none' by default (via
kibana_elasticsearch_ssl_verify). This is poor a security
posture.
This change changes the default value of
'kibana_elasticsearch_ssl_verify' to 'true'.
Change-Id: Ie4fa8e3a60d69cf5c4bdd975030c92be8113ffb1
Closes-Bug: #1885110