KeyVault - /rng response should always return a value on success (#14982)

* Make value required for RandomBytes response

* format

Author: maorleger

specification/keyvault/data-plane/Microsoft.KeyVault/preview/7.3-preview/keys.json

@@ -1289,6 +1289,9 @@
           "description": "The bytes encoded as a base64url string."
         }
       },
+      "required": [
+        "value"
+      ],
       "description": "The get random bytes response object containing the bytes."
     },
     "KeyReleasePolicy": {