Gossipsub update (#1400)

## Issue Addressed

N/A

## Proposed Changes

This provides a number of corrections and improvements to gossipsub. Specifically
- Enables options for greater privacy around the message author
- Provides greater flexibility on message validation
- Prevents unvalidated messages from being gossiped
- Shifts the duplicate cache to a time-based cache inside gossipsub
- Updates the message-id to handle bytes
- Bug fixes related to mesh maintenance and topic subscription. This should improve our attestation inclusion rate.

beacon_node/network/src/router/mod.rs

@@ -297,10 +297,10 @@ impl<T: BeaconChainTypes> Router<T> {
         }
     }
 
-    /// Informs the network service that the message should be forwarded to other peers.
+    /// Informs the network service that the message should be forwarded to other peers (is valid).
     fn propagate_message(&mut self, message_id: MessageId, propagation_source: PeerId) {
         self.network_send
-            .send(NetworkMessage::Propagate {
+            .send(NetworkMessage::Validate {
                 propagation_source,
                 message_id,
             })

beacon_node/network/src/service.rs

@@ -54,9 +54,11 @@ pub enum NetworkMessage<T: EthSpec> {
     },
     /// Publish a list of messages to the gossipsub protocol.
     Publish { messages: Vec<PubsubMessage<T>> },
-    /// Propagate a received gossipsub message.
-    Propagate {
+    /// Validates a received gossipsub message. This will propagate the message on the network.
+    Validate {
+        /// The peer that sent us the message. We don't send back to this peer.
         propagation_source: PeerId,
+        /// The id of the message we are validating and propagating.
         message_id: MessageId,
     },
     /// Reports a peer to the peer manager for performing an action.
@@ -213,7 +215,7 @@ fn spawn_service<T: BeaconChainTypes>(
                         NetworkMessage::SendError{ peer_id, error, id, reason } => {
                             service.libp2p.respond_with_error(peer_id, id, error, reason);
                         }
-                        NetworkMessage::Propagate {
+                        NetworkMessage::Validate {
                             propagation_source,
                             message_id,
                         } => {
@@ -224,7 +226,7 @@ fn spawn_service<T: BeaconChainTypes>(
                                 service
                                     .libp2p
                                     .swarm
-                                    .propagate_message(&propagation_source, message_id);
+                                    .validate_message(&propagation_source, message_id);
                         }
                         NetworkMessage::Publish { messages } => {
                                 let mut topic_kinds = Vec::new();