Subscribe to PeerDAS topics on Fulu fork (#6849)

`TODO(das)` now that PeerDAS is scheduled in a hard fork we can subscribe to its topics on the fork activation. In current stable we subscribe to PeerDAS topics as soon as the node starts if PeerDAS is scheduled.

This PR adds another todo to unsubscribe to blob topics at the fork. This other PR included solution for that, but I can include it in a separate PR
- https://github.com/sigp/lighthouse/pull/5899/files


  Include PeerDAS topics as part of Fulu fork in `fork_core_topics`.

beacon_node/lighthouse_network/src/service/mod.rs

@@ -708,11 +708,17 @@ impl<E: EthSpec> Network<E> {
         }
 
         // Subscribe to core topics for the new fork
-        for kind in fork_core_topics::<E>(&new_fork, &self.fork_context.spec) {
+        for kind in fork_core_topics::<E>(
+            &new_fork,
+            &self.fork_context.spec,
+            &self.network_globals.as_topic_config(),
+        ) {
             let topic = GossipTopic::new(kind, GossipEncoding::default(), new_fork_digest);
             self.subscribe(topic);
         }
 
+        // TODO(das): unsubscribe from blob topics at the Fulu fork
+
         // Register the new topics for metrics
         let topics_to_keep_metrics_for = attestation_sync_committee_topics::<E>()
             .map(|gossip_kind| {