Support cluster status only when the feature is selected

Our netconf topology has unfortunate modeling effects where the implementation-specific (clustered/non-clustered) parts of operational data tree are not separated.

This makes reasoning about the actual model a tad problematic, especially since the update logic is encapsulated in NetconfDeviceTopologyAdapter for both cases.

Separate out the clustered part (which is an add-on) with a if-feature. The clustered topology will then advertize this feature, while base implementation will not.