API Management - Add AZ support to list of v2 limitations

Author: johndowns

articles/api-management/v2-service-tiers-overview.md

@@ -72,6 +72,7 @@ The following API Management capabilities are currently unavailable in the v2 ti
 
 **Infrastructure and networking**
 * Multi-region deployment 
+* Availability zone support
 * Multiple custom domain names 
 * Capacity metric - *replaced by CPU Percentage of Gateway and Memory Percentage of Gateway metrics*
 * Built-in analytics - *replaced by Azure Monitor-based dashboard*