Add tier badge

Add tier badge to Secret Detection page.

doc/user/application_security/secret_detection/index.md

@@ -5,7 +5,7 @@ group: Static Analysis
 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
 ---
 
-# Secret Detection
+# Secret Detection **(FREE)**
 
 > - [Introduced](https://about.gitlab.com/releases/2019/03/22/gitlab-11-9-released/#detect-secrets-and-credentials-in-the-repository) in [GitLab Ultimate](https://about.gitlab.com/pricing/) 11.9.
 > - Made [available in all tiers](https://gitlab.com/gitlab-org/gitlab/-/issues/222788) in 13.3.