Group and user namespaces have the following validation on the api: ^(?!.*\.git$|.*\.atom$|.*[\-._][\-._].*)[a-z0-9][a-z0-9\-_.]*$

Which means they can contain _ but they cannot start with _.

But in the DB there is no limitation for this. So we can make an internal global namespace that will have a slug called _global. Then we can treat global data connectors in a lot less special way.

And when we return data connectors through the API we can remove this slug. The "_global" slug should never actually be exposed to users of the api.

This allows us to have a reserved namespace without needing migrations or having clashes with existing namespaces that may or may not exist in other deployments.