feat: add location-viewer role to datum-cloud viewer assignable role

Grant view access to location resources directly on the viewer
assignable org role rather than through the networking-viewer hierarchy,
since locations are expected to move out of the networking group.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: scotwells

config/assignable-organization-roles/roles/datum-cloud-viewer.yaml

@@ -34,3 +34,5 @@ spec:
       namespace: milo-system
     - name: compute.datumapis.com-viewer
       namespace: milo-system
+    - name: networking.datumapis.com-location-viewer
+      namespace: milo-system