Proposer and attester slashing sse events (sigp#5327)

* default vc to block v3 endpoint and deprecate block-v3 flag

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into unstable

* add proposer and attester event variants

* add TOOOs

* add tests, event triggers

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into proposer-and-attester-slashing-sse-events

* revert

* revert

* remove double event tracking

* Merge branch 'unstable' into proposer-and-attester-slashing-sse-events

* remove todo, fix test

* resolve merge conflicts

* Merge branch 'proposer-and-attester-slashing-sse-events' of https://github.com/eserilev/lighthouse into proposer-and-attester-slashing-sse-events

* leftover debugging

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into proposer-and-attester-slashing-sse-events

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into proposer-and-attester-slashing-sse-events

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -2485,6 +2485,14 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             }
         }
 
+        if let Some(event_handler) = self.event_handler.as_ref() {
+            if event_handler.has_attester_slashing_subscribers() {
+                event_handler.register(EventKind::AttesterSlashing(Box::new(
+                    attester_slashing.clone().into_inner(),
+                )));
+            }
+        }
+
         // Add to the op pool (if we have the ability to propose blocks).
         if self.eth1_chain.is_some() {
             self.op_pool.insert_attester_slashing(attester_slashing)