Return stream for Ipfs::get_providers

[dariusc93]

rust-libp2p merged changes in libp2p/rust-libp2p#2712 that would allow get_providers to return in real time when polling the swarm, so what will likely need to be done is to create a stream when calling Ipfs::get_providers and allow one to poll the stream for the peers found providing the key.

Question:

1. After testing, it looks like i can only call get_providers in libp2p once to receive everything in real time but only up to a specific point (though i will test again since I was checking for a specific key in the swarm). Should we continue to only call it once once this implemented or should we call it on an interval internally?

The event is only emitted until the query is finished earlier or until GetProvidersOk::FinishedWithNoAdditionalRecord is emitted with the ProgressStep::last being true. In this case we will stop the stream once the swarm provide this event.

[dariusc93]

Resolved in 7f2ee70