Create new attribute for Endpoint and Cloud Security

[jmikell821]

Related issue: https://github.com/elastic/security-team/issues/3928

Update the docs/shared/attributes.asciidoc file and create a new attribute, endpoint-cloud-sec with definition of Endpoint and Cloud Security, which replaces the former endpoint-sec attribute. We are retaining the former attribute for use ONLY in versions prior to 8.2.