Add off-protocol value to the bid (#4733)

Add off protocol payment value to the bid instead of relying on the
Builder API. Also disallow this off-protocol payments on P2P bids.

Author: potuz

specs/gloas/beacon-chain.md

@@ -198,6 +198,7 @@ class ExecutionPayloadBid(Container):
     builder_index: ValidatorIndex
     slot: Slot
     value: Gwei
+    execution_payment: Gwei
     blob_kzg_commitments_root: Root
 ```
 

specs/gloas/p2p-interface.md

@@ -281,6 +281,7 @@ The following validations MUST pass before forwarding the
   `BUILDER_WITHDRAWAL_PREFIX` -- i.e.
   `is_builder_withdrawal_credential(state.validators[bid.builder_index].withdrawal_credentials)`
   returns `True`.
+- _[REJECT]_ `bid.execution_payment` is zero.
 - _[IGNORE]_ this is the first signed bid seen with a valid signature from the
   given builder for this slot.
 - _[IGNORE]_ this bid is the highest value bid seen for the corresponding slot