Add DataColumnSidecar gossip topic and message handling (#6147)

* Add `DataColumnSidecar` gossip topic and verification (#5050 and #5783).

* Remove gossip verification changes (#5783).

* Merge branch 'unstable' into data-column-gossip

# Conflicts:
#	beacon_node/beacon_chain/src/data_column_verification.rs
#	beacon_node/beacon_chain/src/lib.rs

* Add gossip cache timeout for data columns. Rename data column metrics for consistency.

* Remove usage of `unimplemented!` and address review comments.

* Remove unnused `GossipDataColumnError` variants and address review comments.

* Merge branch 'unstable' into data-column-gossip

* Update Cargo.lock

* Arc `ChainSpec` in discovery to avoid performance regression when needing to clone it repeatedly.

beacon_node/lighthouse_network/src/peer_manager/peerdb/peer_info.rs

@@ -94,6 +94,15 @@ impl<E: EthSpec> PeerInfo<E> {
                         .syncnets()
                         .map_or(false, |s| s.get(**id as usize).unwrap_or(false))
                 }
+                Subnet::DataColumn(_) => {
+                    // TODO(das): Pending spec PR https://github.com/ethereum/consensus-specs/pull/3821
+                    // We should use MetaDataV3 for peer selection rather than
+                    // looking at subscribed peers (current behavior). Until MetaDataV3 is
+                    // implemented, this is the perhaps the only viable option on the current devnet
+                    // as the peer count is low and it's important to identify supernodes to get a
+                    // good distribution of peers across subnets.
+                    return true;
+                }
             }
         }
         false