Refactor work item counts logic for consolidated list

As we no longer need the tabs at the top of the list pages on the consolidated list view, we can skip that specific query.

We can also use an alternative query to figure out if we need to display a 'no items in namespace' message. The current implementation of this also only works if the page has no pre-applied filters.

If we remove the legacy 'counts' query, we need to re-implement the 'total results' value below the filter bar on the consolidated list.