Add peer score adjustment msgs (#2901)

## Issue Addressed

N/A

## Proposed Changes

This PR adds the `msg` field to `Peer score adjusted` log messages. These `msg` fields help identify *why* a peer was banned.

Example:

```
Jan 11 04:18:48.096 DEBG Peer score adjusted                     score: -100.00, peer_id: 16Uiu2HAmQskxKWWGYfginwZ51n5uDbhvjHYnvASK7PZ5gBdLmzWj, msg: attn_unknown_head, service: libp2p
Jan 11 04:18:48.096 DEBG Peer score adjusted                     score: -27.86, peer_id: 16Uiu2HAmA7cCb3MemVDbK3MHZoSb7VN3cFUG3vuSZgnGesuVhPDE, msg: sync_past_slot, service: libp2p
Jan 11 04:18:48.096 DEBG Peer score adjusted                     score: -100.00, peer_id: 16Uiu2HAmQskxKWWGYfginwZ51n5uDbhvjHYnvASK7PZ5gBdLmzWj, msg: attn_unknown_head, service: libp2p
Jan 11 04:18:48.096 DEBG Peer score adjusted                     score: -28.86, peer_id: 16Uiu2HAmA7cCb3MemVDbK3MHZoSb7VN3cFUG3vuSZgnGesuVhPDE, msg: sync_past_slot, service: libp2p
Jan 11 04:18:48.096 DEBG Peer score adjusted                     score: -29.86, peer_id: 16Uiu2HAmA7cCb3MemVDbK3MHZoSb7VN3cFUG3vuSZgnGesuVhPDE, msg: sync_past_slot, service: libp2p
```

There is also a `libp2p_report_peer_msgs_total` metrics which allows us to see count of reports per `msg` tag. 

## Additional Info

NA

beacon_node/lighthouse_network/tests/pm_tests.rs

@@ -167,7 +167,8 @@ async fn banned_peers_consistency() {
                                 &peer_id,
                                 PeerAction::Fatal,
                                 ReportSource::Processor,
-                                None
+                                None,
+                                ""
                             );
                     },
                     _ => {}