seal single value enum (Azure#23393)

Author: msyyc

specification/keyvault/resource-manager/readme.python.md

@@ -120,3 +120,8 @@ These settings apply only when `--tag=package-2016-10 --python` is specified on
 namespace: azure.mgmt.keyvault.v2016_10_01
 output-folder: $(python-sdks-folder)/keyvault/azure-mgmt-keyvault/azure/mgmt/keyvault/v2016_10_01
 ```
+
+``` yaml $(python)
+modelerfour:
+  seal-single-value-enum-by-default: true
+```