Elasticsearch support for _FILE environment variables breaks ECK readiness proble

[pebrc]

elastic/elasticsearch#47573

Introduces support for _FILE environment variables but also introduces strict permission checks on the files. ECK uses PROBE_PASSWORD_FILE for the Elasticsearch readiness probe and fails subsequently the permissions check.

Either rename the variable (because we don't want to the expose this to Elasticsearch) or fix the permissions.

See also elastic/elasticsearch#49653