Enhance the network configuration with shared keyring

Today, when a peer shares a keyring with another peer, it passively waits for a peer document receival where it will see another peer has the key.

But we could have more active behavior, where the local peer, when we change its keyring:

• looks in its database if it already knows a different peer than itself with the same pubkey
• eventually looks in the network if a peer with the same pubkey exists (using /peers URL)