Adds a new HTTP endpoint that can be used to request records for the
closest peers to a given key that the routing implementation knows
about.

The use-case for this is browser nodes performing random walks to
find peers that they can make a circuit relay reservation on, without
having to be DHT clients to perform the walk which can be undesirable
given all the connection/processing overhead that entails.

Co-authored-by: Guillaume Michel <guillaumemichel@users.noreply.github.com>