Add ci_archive_traces_cron_worker configuration to gitlab.yml.example

changelogs/unreleased/add-ci_archive_traces_cron_worker-to-gitlab-yml.yml

+---
+title: Add an example of the configuration of archive trace cron worker in gitlab.yml.example
+merge_request: 20583
+author:
+type: other

config/gitlab.yml.example

@@ -261,6 +261,9 @@ production: &base
     # once per hour you will have concurrent 'git fsck' jobs.
     repository_check_worker:
       cron: "20 * * * *"
+    # Archive live traces which have not been archived yet
+    ci_archive_traces_cron_worker:
+      cron: "17 * * * *"
     # Send admin emails once a week
     admin_email_worker:
       cron: "0 0 * * 0"