add cache purge ps and cli articles

Author: duongau

articles/frontdoor/TOC.yml

@@ -251,7 +251,13 @@
         - name: Rules Engine
           href: standard-premium/how-to-configure-rule-set.md
         - name: Purge cache
-          href: standard-premium/how-to-cache-purge.md
+          items:
+          - name: Azure portal
+            href: standard-premium/how-to-cache-purge.md
+          - name: Azure PowerShell
+            href: standard-premium/how-to-cache-purge-powershell.md
+          - name: Azure CLI
+            href: standard-premium/how-to-cache-purge-cli.md
         - name: Compression
           href: standard-premium/how-to-compression.md
       - name: Enable Private Link to secure origins