[Merge] Optimistic Sync: Stage 1 (#2686)

* Add payload verification status to fork choice

* Pass payload verification status to import_block

* Add valid back-propagation

* Add head safety status latch to API

* Remove ExecutionLayerStatus

* Add execution info to client notifier

* Update notifier logs

* Change use of "hash" to refer to beacon block

* Shutdown on invalid finalized block

* Tidy, add comments

* Fix failing FC tests

* Allow blocks with unsafe head

* Fix forkchoiceUpdate call on startup

consensus/proto_array/src/error.rs

@@ -30,4 +30,8 @@ pub enum Error {
         head_justified_epoch: Epoch,
         head_finalized_epoch: Epoch,
     },
+    InvalidAncestorOfValidPayload {
+        ancestor_block_root: Hash256,
+        ancestor_payload_block_hash: Hash256,
+    },
 }