Merge branch 'fix/doc-api-i' into 'master'

Edit API docs for consistency

See merge request gitlab-org/gitlab!69688

doc/api/instance_clusters.md

@@ -4,7 +4,7 @@ group: Configure
 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 clusters API **(FREE)**
+# Instance clusters API **(FREE SELF)**
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/36001) in GitLab 13.2.
 

doc/api/instance_level_ci_variables.md

@@ -4,7 +4,7 @@ group: Pipeline Authoring
 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 CI/CD variables API
+# Instance-level CI/CD variables API **(FREE SELF)**
 
 > - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/14108) in GitLab 13.0
 > - [Feature flag removed](https://gitlab.com/gitlab-org/gitlab/-/issues/218249) in GitLab 13.2.

doc/api/issue_links.md

@@ -6,7 +6,7 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 # Issue links API **(FREE)**
 
-> The simple "relates to" relationship [moved](https://gitlab.com/gitlab-org/gitlab/-/issues/212329) to [GitLab Free](https://about.gitlab.com/pricing/) in 13.4.
+> The simple "relates to" relationship [moved](https://gitlab.com/gitlab-org/gitlab/-/issues/212329) to GitLab Free in 13.4.
 
 ## List issue relations