When creating the keystore explicitly (from executing
elasticsearch-keystore create) or implicitly (for plugins that require
the keystore to be created on install) on an Elasticsearch package
installation, we are running as the root user. This leaves
/etc/elasticsearch/elasticsearch.keystore having the wrong ownership
(root:root) so that the elasticsearch user can not read the keystore on
startup. This commit adds setgid to /etc/elasticsearch on package
installation so that when executing this directory (as we would when
creating the keystore), we will end up with the correct ownership
(root:elasticsearch). Additionally, we set the permissions on the
keystore to be 660 so that the elasticsearch user via its group can read
this file on startup.
Relates #26412
7a035f5f84