Do not use env variables ending in _FILE with Elasticsearch

[pebrc]

*_FILE variables will interpreted as file paths and be read by
Elasticsearch as of v8.0 and are required to have strict read-only permissions.

Fixes #2177 (or rather works around it)

Will raise an issue against the Elasticsearch repo as well because on k8s even when using restricted SecretVolume permissions the file the variable points to is a symlink with 0777 permissions and only the file it is pointing to has the requested restricted permisssions with 0600 or 0400.

[root@cluster1-es-default-0 elasticsearch]# ls -l /mnt/elastic-internal/probe-user/
total 0
lrwxrwxrwx 1 root root 29 Nov 27 15:55 elastic-internal-probe -> ..data/elastic-internal-probe
[root@cluster1-es-default-0 elasticsearch]# ls -l /mnt/elastic-internal/probe-user/..data/elastic-internal-probe 
-rw------- 1 root root 24 Nov 27 15:55 /mnt/elastic-internal/probe-user/..data/elastic-internal-probe

[sebgl]

A rolling upgade of all Elasticsearch clusters should be triggered when upgrading ECK to a version including this commit. Which is probably fine.