Set 'defaultPlatform: linux' frontmatter for a page

Author: Simran-B

content/actions/hosting-your-own-runners/configuring-the-self-hosted-runner-application-as-a-service.md

@@ -6,6 +6,7 @@ redirect_from:
 versions:
   free-pro-team: '*'
   enterprise-server: '>=2.22'
+defaultPlatform: linux
 ---
 
 {% data reusables.actions.enterprise-beta %}