Add payload attestation to op pool and pack into block (#9180)

Store gossip-verified `PayloadAttestationMessage`s in the operation pool and pack them into the block body at during block production.

Built on top of #9145.


  


Co-Authored-By: Jimmy Chen <jchen.tc@gmail.com>

beacon_node/operation_pool/src/persistence.rs

@@ -209,6 +209,7 @@ impl<E: EthSpec> PersistedOperationPool<E> {
             proposer_slashings,
             voluntary_exits,
             bls_to_execution_changes: RwLock::new(bls_to_execution_changes),
+            payload_attestation_messages: Default::default(),
             reward_cache: Default::default(),
             _phantom: Default::default(),
         };