Make Tor aware of the top-30 destinations of Tor Exit traffic

This ticket is to make Tor aware of the top-30 destinations of Tor Exit traffic, by defining a destination such as "the aggregation of the autonomous system numbers of a specific organization" .

This could require each Tor instance to have an in-memory awareness of, let's say first top 500 destination AS numbers to which he's sending Tor Exit traffic, aggregating them by the owner (es: "Facebook" or "Google"), then with some magic privacy-aware protocol share it with some measurement collection authority that elaborate the "Tor network top 30 destinations by amount of traffic", that get authenticated by some kind of consensus and made it publicly available.

The privacy impact and relevant security risk assessment must be done, understanding effectively what can be measured without harming end-users.