Merge devnet 3 (#2859)

## Issue Addressed

N/A

## Proposed Changes

Changes required for the `merge-devnet-3`. Added some more non substantive renames on top of @realbigsean 's commit. 
Note: this doesn't include the proposer boosting changes in kintsugi v3.

This devnet isn't running with the proposer boosting fork choice changes so if we are looking to merge https://github.com/sigp/lighthouse/pull/2822 into `unstable`, then I think we should just maintain this branch for the devnet temporarily. 


Co-authored-by: realbigsean <seananderson33@gmail.com>
Co-authored-by: Paul Hauner <paul@paulhauner.com>

beacon_node/execution_layer/src/test_utils/handle_rpc.rs

@@ -62,12 +62,12 @@ pub async fn handle_rpc<T: EthSpec>(
                     ExecutePayloadResponseStatus::Valid => ExecutePayloadResponse {
                         status,
                         latest_valid_hash: Some(request.block_hash),
-                        message: None,
+                        validation_error: None,
                     },
                     ExecutePayloadResponseStatus::Syncing => ExecutePayloadResponse {
                         status,
                         latest_valid_hash: None,
-                        message: None,
+                        validation_error: None,
                     },
                     _ => unimplemented!("invalid static executePayloadResponse"),
                 }