Allow access to Azure services
这个参数会控制VNET访问这个MysqL。如果是YES, vnet的VM可以访问MysqL
如果是NO， 如果VM访问会有提示报错：
ERROR 9009 (28000): Client from Azure Virtual Networks is not allowed to access the server. Please make sure your Virtual Network is correctly configured.
解决的方式是配置vnet service endpoint
