doc(etcd-maintenance): add reference to etcd-defrag CronJob (#43394)

* doc(etcd-maintenance): add reference to etcd-defrag CronJob

* doc: improve style according to style guide

* chore: fix file name

Author: clementnuss

content/en/docs/tasks/administer-cluster/configure-upgrade-etcd.md

@@ -416,4 +416,8 @@ Defragmentation is an expensive operation, so it should be executed as infrequen
 as possible. On the other hand, it's also necessary to make sure any etcd member
 will not run out of the storage quota. The Kubernetes project recommends that when
 you perform defragmentation, you use a tool such as [etcd-defrag](https://github.com/ahrtr/etcd-defrag).
+
+You can also run the defragmentation tool as a Kubernetes CronJob, to make sure that
+defragmentation happens regularly. See [`etcd-defrag-cronjob.yaml`](https://github.com/ahrtr/etcd-defrag/blob/main/doc/etcd-defrag-cronjob.yaml)
+for details. 
 {{< /note >}}