Adding totalCount to transactionList result (#14858)

Author: muazmian

specification/billing/resource-manager/Microsoft.Billing/stable/2020-05-01/billing.json

@@ -5729,6 +5729,12 @@
             "$ref": "#/definitions/Transaction"
           }
         },
+        "totalCount": {
+          "description": "Total number of records.",
+          "type": "number",
+          "format": "int32",
+          "readOnly": true
+        },
         "nextLink": {
           "description": "The link (url) to the next page of results.",
           "type": "string",