Broadcast address changes at Capella (#3919)

* Add first efforts at broadcast

* Tidy

* Move broadcast code to client

* Progress with broadcast impl

* Rename to address change

* Fix compile errors

* Use `while` loop

* Tidy

* Flip broadcast condition

* Switch to forgetting individual indices

* Always broadcast when the node starts

* Refactor into two functions

* Add testing

* Add another test

* Tidy, add more testing

* Tidy

* Add test, rename enum

* Rename enum again

* Tidy

* Break loop early

* Add V15 schema migration

* Bump schema version

* Progress with migration

* Update beacon_node/client/src/address_change_broadcast.rs

Co-authored-by: Michael Sproul <micsproul@gmail.com>

* Fix typo in function name

---------

Co-authored-by: Michael Sproul <micsproul@gmail.com>

beacon_node/client/src/builder.rs

@@ -1,3 +1,4 @@
+use crate::address_change_broadcast::broadcast_address_changes_at_capella;
 use crate::config::{ClientGenesis, Config as ClientConfig};
 use crate::notifier::spawn_notifier;
 use crate::Client;
@@ -802,6 +803,25 @@ where
                     // Spawns a routine that polls the `exchange_transition_configuration` endpoint.
                     execution_layer.spawn_transition_configuration_poll(beacon_chain.spec.clone());
                 }
+
+                // Spawn a service to publish BLS to execution changes at the Capella fork.
+                if let Some(network_senders) = self.network_senders {
+                    let inner_chain = beacon_chain.clone();
+                    let broadcast_context =
+                        runtime_context.service_context("addr_bcast".to_string());
+                    let log = broadcast_context.log().clone();
+                    broadcast_context.executor.spawn(
+                        async move {
+                            broadcast_address_changes_at_capella(
+                                &inner_chain,
+                                network_senders.network_send(),
+                                &log,
+                            )
+                            .await
+                        },
+                        "addr_broadcast",
+                    );
+                }
             }
 
             start_proposer_prep_service(runtime_context.executor.clone(), beacon_chain.clone());