Expose Pulsar healthcheck about pulsar-rs

[Geal]

so this should work with f43186c, but there will not be a global healthcheck method: the server we connect to with the client might not be the one we connect to when creating a producer or consumer, so right now, the check_connection() method is available on the producer and consumer objects.
It's probably not good enough in the general case though, because multiple producers and consumers could be using the same TCP connection, but ping messages are global on a connection.
So a better solution might be to expose a stream of "pong" for a connection, and the producers and consumers on it could share that stream (and any of them could ping as needed)

[KannarFr]

For the usage of vector I think it's enough yet. Can you do a release of with it?

[Geal]

done in 1.0 release