external_services: add NoNamespace option to the List method
Created by: unknwon
The new NoNamespace
option allow listing external services under no particular namespace (i.e. site-level external services owned by all site admins).
This option is then used in handling config overrides of external services from config file. This approach has the minimal change without listing any user-added external services (which are not used in the process of config overrides).
Easier to review by commit.
Part of #12760.