Improve 'dht routing' design to accomodate router-specific features

[guseggert]

Checklist

• My issue is specific & actionable.
• I am not suggesting a protocol enhancement.
• I have searched on the issue tracker for my issue.

Description

Kubo recently generalized its content routing to be able to use arbitrary content routers that satisfy the libp2p routing interface. This enables Kubo users to experiment with other content routers than the traditional Kademlia DHT. The core functionality works, but some peripheral functionality is broken as a result:

• ipfs stats dht
• ipfs dht query
• Possibly AutoRelay when using custom router type

There might be other things that are broken too that we haven't found yet.

The code for constructing this also very complex and hard to understand, contributing to the bugginess.

Fundamentally this is because there are assumptions in certain commands and functionality that there's always a Kademlia DHT available, which is no longer true.

[guillaumemichel]

Related to ipfs/go-ipfs-provider#49 and libp2p/go-libp2p#2175