Merge branch 'docs-fix-h1-instance-level-clusters' into 'master'

Docs: H1 tier info for instance-level clusters

See merge request gitlab-org/gitlab!70797

doc/user/instance/clusters/index.md

@@ -4,7 +4,7 @@ group: unassigned
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 ---
 
-# Instance-level Kubernetes clusters
+# Instance-level Kubernetes clusters **(FREE SELF)**
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/39840) in GitLab 11.11.