{Storage} change modelAsString from false to true (#13073)

Author: Juliehzl

specification/storage/resource-manager/Microsoft.Storage/stable/2021-01-01/file.json

@@ -215,7 +215,7 @@
             ],
             "x-ms-enum": {
               "name": "ListSharesExpand",
-              "modelAsString": false
+              "modelAsString": true
             },
             "description": "Optional, used to expand the properties within share's properties."
           }
@@ -286,7 +286,7 @@
             ],
             "x-ms-enum": {
               "name": "PutSharesExpand",
-              "modelAsString": false
+              "modelAsString": true
             },
             "description": "Optional, used to create a snapshot."
           },