Alternative Content Routing

Currently, go-ipfs searches the default router (usually the DHT) for providers when trying to find content. However, for certain content, there may be better ways to do this.

I'd like to be able to:

1. Disable searching the DHT.
2. Try (repeatedly?) to connect to specific peers.
3. Use pubsub. We may have situations where content is all related to some "topic" but not all in the same DAG. Nodes interested in related data can join this pubsub topic and use gossipsub's network forming.