Rperezzamora/small fix for short codes (#16554)

* making numberType on ShortCode model object extensible enum

* Revert "making numberType on ShortCode model object extensible enum"

This reverts commit 5051e3e.

Reverting change since it should have been done on feature branch

* adding extensible enum metadata to short code numbertype

Author: rperezzamora

specification/communication/data-plane/ShortCodes/preview/2021-10-25-preview/shortcodes.json

@@ -316,7 +316,11 @@
             "shortCode",
             "alphaId"
           ],
-          "type": "string"
+          "type": "string",
+          "x-ms-enum": {
+            "name": "NumberType",
+            "modelAsString": true
+          }
         },
         "countryCode": {
           "description": "ISO 3166 2-char code representing the country e.g. 'US'.",