List a newsletter's tags

The newsletter's live audience tags, alphabetical, each with a count of currently subscribed holders. Needs audience: read: how a creator segments their audience is not public.

Retired tags are excluded by default. A tag that an already sent article was addressed to cannot be deleted outright, because the audience of a sent article does not change retroactively, so it is retired instead and keeps its assignments. Pass include_retired=true to see those when rendering the audience of a historical article.