* [DOCS] Add ES security principles
* Incorporating review feedback
* More changes from review feedback
* Fix cross-link to Painless guide
* Clarify callout text
* Add information about elasticsearch user
* Minor wording edits
* Consolidate Java Security Manager description, plus other edits
* Clarify not running as root
Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
Adam Locke