Finish transition to the new PeerIds format

[tomaka]

Internally, PeerIds are now both an identity-multihash of the public key and a SHA256-multihash of that public key.

For Kademlia purposes, we use the SHA256 version.
All PeerIds are also displayed to the user as the SHA256 version.

The end goal is to transition these two to the identity version.

As a first step, we should show PeerIds to the user through their identity versions, so that all the configurations can be updated.

[tomaka]

cc libp2p/rust-libp2p#1576

There are two approaches:

• Change the Display implementation of PeerId to the new one in libp2p.
• In Substrate, change everywhere we print a PeerId to show the identity version by manually base58-encoding the multihash. The problem with that approach is that we might miss some locations.

[romanb]

When nodes using libp2p-kad are eventually upgraded, there will inevitably be a period where nodes have two identities in the DHT, right (assuming you don't stop and upgrade all your nodes at once but do a rolling upgrade)?

[tomaka]

I think the final step towards this is to remove support for the old representation.

While this will create a mild incompatibility between nodes regarding Kademlia, I don't think it is problematic. The random discovery should continue to work (albeit in an awkward way), and the authority-discovery is "best effort" mechanism and is not critical for the network to function properly.

[tomaka]

I think the final step towards this is to remove support for the old representation.

Of course we should wait for a couple month to do that.

[tomaka]

#6064 is in Polkadot 0.8.0 but not in versions 0.7.x.

According to the telemetry, there are currently only 9 Kusama nodes left that are on versions 0.7.x and that are in sync. Notably, there are quite a few nodes on versions 0.7.x and that seem to be stuck. I think it is reasonable for users to expect that versions 0.7.x no longer work properly.

I believe that we could finish this now.

[kaichaosun]

No sure if it's related to this issue #7082.

[romanb]

This should be complete with #7077 which includes libp2p/rust-libp2p#1608.