Add free tier badge

Add Free tier badge to Database-related update pages.

doc/update/mysql_to_postgresql.md

@@ -4,7 +4,7 @@ group: Database
 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
 ---
 
-# Migrating from MySQL to PostgreSQL
+# Migrating from MySQL to PostgreSQL **(FREE SELF)**
 
 This guide documents how to take a working GitLab instance that uses MySQL and
 migrate it to a PostgreSQL database.

doc/update/upgrading_postgresql_using_slony.md

@@ -4,7 +4,7 @@ group: Database
 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
 ---
 
-# Upgrading PostgreSQL Using Slony
+# Upgrading PostgreSQL Using Slony **(FREE SELF)**
 
 This guide describes the steps one can take to upgrade their PostgreSQL database
 to the latest version without the need for hours of downtime. This guide assumes