changing to Azure Monitor metric retention rules

Due to a CRI https://msazure.visualstudio.com/One/_workitems/edit/6952598 where a customer was confused by these differing rules.

Author: rboucher

articles/app-service/web-sites-monitor.md

@@ -5,7 +5,7 @@ author: btardif
 
 ms.assetid: d273da4e-07de-48e0-b99d-4020d84a425e
 ms.topic: article
-ms.date: 01/11/2019
+ms.date: 04/23/2020
 ms.author: byvinyal
 ms.custom: seodec18
 
@@ -130,11 +130,7 @@ There are two metrics that reflect CPU usage:
 **CPU percentage**: Useful for apps hosted in Basic, Standard, and Premium plans, because they can be scaled out. CPU percentage is a good indication of the overall usage across all instances.
 
 ## Metrics granularity and retention policy
-Metrics for an app and app service plan are logged and aggregated by the service, with the following granularities and retention policies:
-
-* **Minute** granularity metrics are kept for 30 hours.
-* **Hour** granularity metrics are kept for 30 days.
-* **Day** granularity metrics are kept for 30 days.
+Metrics for an app and app service plan are logged and aggregated by the service and [retained according to these rules](../azure-monitor/platform/data-platform-metrics.md#retention-of-metrics).
 
 ## Monitoring quotas and metrics in the Azure portal
 To review the status of the various quotas and metrics that affect an app, go to the [Azure portal](https://portal.azure.com).
@@ -167,4 +163,4 @@ For more information about autoscale, see [How to scale](../monitoring-and-diagn
 <!-- Images. -->
 [http403]: ./media/web-sites-monitor/http403.png
 [quotas]: ./media/web-sites-monitor/quotas.png
-[metrics]: ./media/web-sites-monitor/metrics.png
+[metrics]: ./media/web-sites-monitor/metrics.png