Add support for the 'query' endpoint

[jacobheun]

The query endpoint on the IPFS api allows you to find the closest peers on the network to a given PeerId. We should leverage this to implement the getClosestPeers function with a matching api to the dht's method, https://github.com/libp2p/js-libp2p-kad-dht/blob/v0.20.1/src/peer-routing/index.js#L209.

This will allow nodes using delegate routers to find their closest peers on the network and connect to them, so that they can learn its addresses. This is critical for peers to be able to find one another via the dht.

Relates to libp2p/js-libp2p#704