[Built-in Rule] Auditing on SQL server should be enabled

Azure policy: https://github.com/Azure/azure-policy/blob/master/built-in-policies/policyDefinitions/SQL/SqlServerAuditing_Audit.json

``` javascript
{
"name": "SQL_Auditing_Enabled",
"description": "Auditing on SQL server should be enabled",
"recommendation": "Enable auditing on your SQL Server",
"helpUri": "https://github.com/Azure/template-analyzer/docs/built-in-bpa-rules.md/#auditing-on-sql-server-should-be-enabled",
"parameters": {
"setting": "defaultSetting"
},
"evaluation": {
"resourceType": "Microsoft.Sql/servers",
"where": {
"path": "kind",
"regex": "^((?!analytics).)*$"
},
"evaluate": {
"resourceType": "Microsoft.Sql/servers/auditingSettings",
"path": "properties.auditingSettings.state",
"equals": "[parameters('setting')]"
}
}
```