[engine]: support consuming geoip data from the mobile client

We should support consuming geoip data from the mobile client in the engine. This is part of the bigger plan to ship the geoip database as part of the mobile apps and remove it from the engine build. See http://github.com/ooni/probe/issues/2828. To this end, we need to make changes to the oonimkall API surface to accept geoip related configuration from the mobile clients.