[Backport 2.x] Adds findings alerts legend in overview page#321

AWSHurneyt merged 1 commit into2.xopensearch-project/security-analytics-dashboards-plugin:2.xfrom

backport/backport-318-to-2.xopensearch-project/security-analytics-dashboards-plugin:backport/backport-318-to-2.xCopy head branch name to clipboard