Remove VPN gateways from the tags unsupported list

Author: flanakin

articles/cost-management-billing/costs/understand-cost-mgt-data.md

@@ -121,7 +121,6 @@ If you do not see a specific tag in Cost Management, consider the following:
     - Notification Hubs
     - Service Bus
     - Time Series Insights
-    - VPN gateway
 
 Here are a few tips for working with tags: