P2P: add wrapper/abstraction for known peers

[CHr15F0x]

Instead of referring directly to libp2p::kad for known peers consider creating a wrapper that would hold the list of known peers. The "list" would:

• include "in-config" predefined peers (which ofc should also be in the local DHT)
• be in sync with any kad updates (in particular new peers)

Pros:

• syncing would proceed immediately provided that at least one peer was predefined via config,
• internal p2p client logic wouldn't have to periodically poll for new/random peers.

Also see: #2187