Move node name registry to each module

[MegaRedHand]

We currently have a name registry mapping the peer ID to its name (loaded from the configuration at startup) in a static variable with an RwLock. We should instead keep this hashmap inside the P2P struct, for simplicity. This reduces global state and would also allow us to more easily add node names to logs (instead of the opaque peer IDs).

After doing this, we can replicate it in other modules, for example, to map from validator ID to node name.