Scope: read:lettings-website

The V2 copy of network.api's GET api/lettings-properties/search-stats, with the same
fields and names, for setting a search form's ranges. It counts what the website search
shows with no filters.

• teamIds replaces teamAPIList: team ids, not other teams' API keys. It
  narrows to those teams, and each must be one the key can reach, or the request answers
  403. A team key always reads its own team.
• When nothing is listed, every figure is 0. network.api answered an empty body.
• Added in V2: minBathrooms and maxBathrooms, and propertyTypes, the
  property types in stock with their display names and counts, in name order. Each
  value is what the search's propertyTypes filter takes.

Not here yet: towns and counties (ENG-6740).