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/mod.rs

@@ -1027,6 +1027,10 @@ impl<E: EthSpec> PeerManager<E> {
                                 .or_default()
                                 .insert(id);
                         }
+                        // TODO(das) to be implemented. We're not pruning data column peers yet
+                        // because data column topics are subscribed as core topics until we
+                        // implement recomputing data column subnets.
+                        Subnet::DataColumn(_) => {}
                     }
                 }
             }