[ReleasePR postgresql] Add optional param - private DNS zone to server API (#1586)

Create to sync Azure/azure-rest-api-specs#13716
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/master...AzureSDKAutomation:sdkAuto/postgresql?expand=1)

Author: msftbot[bot]

schemas/2020-02-14-preview/Microsoft.DBforPostgreSQL.json

@@ -348,6 +348,16 @@
           "format": "date-time",
           "description": "Restore point creation time (ISO8601 format), specifying the time to restore from."
         },
+        "privateDnsZoneArguments": {
+          "oneOf": [
+            {
+              "$ref": "#/definitions/ServerPropertiesPrivateDnsZoneArguments"
+            },
+            {
+              "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
+            }
+          ]
+        },
         "sourceResourceGroupName": {
           "type": "string",
           "description": "The resource group name of source serve PostgreSQL server name to restore from."
@@ -413,6 +423,15 @@
         }
       }
     },
+    "ServerPropertiesPrivateDnsZoneArguments": {
+      "type": "object",
+      "properties": {
+        "privateDnsZoneArmResourceId": {
+          "type": "string",
+          "description": "private dns zone arm resource id."
+        }
+      }
+    },
     "Sku": {
       "type": "object",
       "properties": {