chore: refactor listen_to handler as alisten_to and make POST v3/ async

[viniarck]

There's opportunity in the future to refactor the current decorated on_topology_event handler with alisten_to instead, and then also make the POST v3/ endpoint async, the main benefit would also be able to remove the self._lock since we wouldn't have tasks yields happening, while also being having liighter handlers, the roadblock to address this chore here is also refactor the unit tests issue #50 to be async compatible, until we get there, in the meantime, it's easier to leverage dynamic_single thread mode on listen_to instead kytos-ng/kytos#399.