collect and archive DNS resolver data of tor exits

context: https://medium.com/@nusenu/who-controls-tors-dns-traffic-a74a7632e8ca

" 5. Add DNS related information to Relay Search (a long term item)

It would be nice and probably effective to have information about DNS resolvers show up on Relay Search, because it is a popular tool for relay operators to check on their relay state. Operators could easily see if they use any less desirable DNS resolvers if that information is shown on Relay Search. That way we could even reach operators who have no or invalid ContactInfo data, but multiple steps are required before this could happen: The currently unavailable data needs to be

collected and regularly updated

"