Update Error Code to string (#24150)

Author: prchalla1

specification/cost-management/resource-manager/Microsoft.CostManagement/preview/2023-04-01-preview/common-types.json

@@ -87,8 +87,7 @@
       "properties": {
         "code": {
           "description": "Error code.",
-          "type": "integer",
-          "format": "int32",
+          "type": "string",
           "readOnly": true
         },
         "message": {

specification/cost-management/resource-manager/Microsoft.CostManagement/preview/2023-04-01-preview/examples/GenerateDetailedCostReportOperationStatusBySubscriptionScope.json

@@ -16,7 +16,7 @@
           "validTill": "2020-12-08T05:55:59.4394737Z"
         },
         "error": {
-          "code": 0,
+          "code": "0",
           "message": null
         }
       }