[DOCS] Integrate information about ABAC

[elasticmachine]

Original comment by @lcawl:

Information about attribute-based access control needs to be added to the security documentation. There is currently information in:
https://www.elastic.co/blog/attribute-based-access-control-with-xpack
LINK REDACTED

[jrodewig]

[docs issue triage]
Leaving open. Still relevant.

Here's where we currently link to the ABAC blog post:
https://www.elastic.co/guide/en/elasticsearch/reference/master/authorization.html#attributes

[dedemorton]

It seems really strange to link to a 6.1 blog post in our current docs. I wonder if it's possible to get the blog itself updated to be more version agnostic (maybe give a range of versions) while you're waiting for the content to land in the guide.