Update exists annotation test to be more real world oriented

[praveenrewar]

The current example used for testing exists annotation consists of a Namespace and a ConfigMap where the ConfigMap is an external resource with the exists annotation. In the app there is no resource that depends on the ConfigMap, hence the example doesn't depict the correct use case for the exists annotation.

The example is technically correct but I felt like it can be improved a little bit. So instead of the ConfigMap, I used the Namespace as an external resource, and since the ConfigMap is supposed to be created inside that Namespace, it actually needs it to exists.