adding monitoring horizontal marking

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cc: @msmbaldwin

Author: rboucher

articles/key-vault/general/monitor-key-vault.md

@@ -10,6 +10,7 @@ ms.subservice: general
 ms.topic: how-to
 ms.date: 09/21/2021
 ms.author: mbaldwin
+ms.custom: subject-monitoring
 # Customer intent: As a key vault administrator, I want to learn the options available to monitor the health of my vaults
 ---