Attempt to delete a workspace namespace even if the namespace is not managed

[metlos]

Describe the bug

A confusing error message in the logs after a workspace delete.

Che version

latest

Steps to reproduce

1. Set up Che with default configuration, namely <username>-che as the namespace default (or actually any value not containing <workspaceid>)
2. Create a workspace
3. Delete the workspace
4. Observe a warning in the logs claiming that the namespace/project cannot be deleted because it is not managed.

Expected behavior

No message in the logs, because the namespace is indeed not managed so Che should not even try to delete it.