Splitting this request from T401274.

Editors should be able to unwatchlist pages by namespace, for example only Draft namespace pages.

This could be a single or multi-select feature, but given the potential for mistakes with this tool, it might make sense to limit this to one namespace at a time, to encourage editors to proceed with caution and do one namespace at a time.

This could be a filter that is grouped with the 'Edited in X days' filter, so that users can combine the filters and remove, for example, all Template pages not edited in the last 180 days.