Allow for mounting of CA for OIDC communication from ECK

Following this guide https://www.elastic.co/guide/en/elasticsearch/reference/7.9/oidc-guide-authentication.html#oidc-ssl-config

The elasticsearch-kibana helm chart requires the ability to mount something like a secret into the Elasticsearch containers, and add to the OIDC setup to specify a certificate_authority for the SSL communication.

Blocked by https://repo1.dso.mil/platform-one/big-bang/apps/core/elasticsearch-kibana/-/issues/13