chore(docs): remove namespace for cluster scope resource (#637)

Author: Henni

website/docs/docs/concepts/00-resource-group-definitions.md

@@ -28,7 +28,7 @@ consistent, controlled way.
 
 A ResourceGraphDefinition, like any Kubernetes resource, consists of three main parts:
 
-1. **Metadata**: name, namespace, labels, etc.
+1. **Metadata**: name, labels, etc.
 2. **Spec**: Defines the structure and properties of the ResourceGraphDefinition
 3. **Status**: Reflects the current state of the ResourceGraphDefinition
 
@@ -313,4 +313,4 @@ status:
   topologicalOrder:
     - configmap
     - deployment
-```
+```