WIP State level WatchInterfaces

Wraps the State level WatchInterfaces watcher, and maps the Ids we get from state into Tags for the API.

This also includes exposing the WatchInterfaces call in the API, so touching state/apiserver and state/api
FWIW, I would generally prefer to see positive terms than negative ones -- `!disabled` is a really cumbersome way to write "enabled", compared to `!enabled` for "disabled".