Implement engine API v1.0.0-alpha.4 (#2810)

* Added ForkchoiceUpdatedV1 & GetPayloadV1

* Added ExecutePayloadV1

* Added new geth test vectors

* Separated Json Object/Serialization Code into file

* Deleted code/tests for Requests Removed from spec

* Finally fixed serialization of null '0x'

* Made Naming of JSON Structs Consistent

* Fix clippy lints

* Remove u64 payload id

* Remove unused serde impls

* Swap to [u8; 8] for payload id

* Tidy

* Adjust some block gen return vals

* Tidy

* Add fallback when payload id is unknown

* Remove comment

Co-authored-by: Mark Mackey <mark@sigmaprime.io>

beacon_node/beacon_chain/src/errors.rs

@@ -183,6 +183,8 @@ pub enum BlockProductionError {
     ExecutionLayerMissing,
     TerminalPoWBlockLookupFailed(execution_layer::Error),
     GetPayloadFailed(execution_layer::Error),
+    FailedToReadFinalizedBlock(store::Error),
+    MissingFinalizedBlock(Hash256),
 }
 
 easy_from_to!(BlockProcessingError, BlockProductionError);