Move the peer manager to be a behaviour (#2773)

This simply moves some functions that were "swarm notifications" to a network behaviour implementation.

Notes
------
- We could disconnect from the peer manager but we would lose the rpc shutdown message
- We still notify from the swarm since this is the most reliable way to get some events. Ugly but best for now
- Events need to be pushed with "add event" to wake the waker

Co-authored-by: Divma <26765164+divagant-martian@users.noreply.github.com>

beacon_node/lighthouse_network/src/lib.rs

@@ -68,6 +68,7 @@ pub use behaviour::{BehaviourEvent, Gossipsub, PeerRequestId, Request, Response}
 pub use config::Config as NetworkConfig;
 pub use discovery::{CombinedKeyExt, EnrExt, Eth2Enr};
 pub use discv5;
+pub use libp2p;
 pub use libp2p::bandwidth::BandwidthSinks;
 pub use libp2p::gossipsub::{MessageAcceptance, MessageId, Topic, TopicHash};
 pub use libp2p::{core::ConnectedPoint, PeerId, Swarm};