net: Use genesis-based kad protocol for discovery and deprecate /sup/kad

[lexnv]

This PR replaces the /dot/kad p2p network protocol used for discovery with the genesis-based equivalent /91b171bb158e2d3848fa23a9f1c25182fb8e20313b2c1eb49219da7a70ce90c3/kad.

The genesis-based protocol was used for quite a while to discover substrate-based chains and the spec was not updated to reflect that.

The /dot/kad is no longer included as a fallback protocol (like other protocols do), to facilitate the deprecation of the legacy protocols. This has a few advantages:

• Untangle the networks -- the current DHT of polkadot may contain nodes not responding to substrate protocols. They can be network scrapers (like Polkawatch which uses https://github.com/lexnv/subp2p-explorer), or they can be nodes part of an entirely different network.
• Reduce the complexity of substrate networking code and improve maintenance -- the code to facilitate fallbacks is not entirely trivial. For example, litep2p has a complete graph architecture to enable any protocols to interact with each other in case of fallbacks.

Deprecation plan:

1. Include in DHT only nodes that contain genesis-based KAD protocols
2. Remove /dot/kad support for substrate nodes
3. Create a followup PR to remove other /dot/.. legacy protocols
4. Remove /dot/.. legacy protocols support for substrate nodes
5. Clean-up fallback support in substrate

In response to: paritytech/polkadot-sdk#3833

cc @dmitry-markin @bkchr @skunert

[bkchr]

@Noc2 can you merge this?

[Noc2]

Done. Thanks for pinging me.