Add more checks and logging before genesis (#4730)

## Proposed Changes

This PR adds more logging prior to genesis, particularly on networks that start with execution enabled.

There are new checks using `eth_getBlockByHash/Number` to verify that the genesis state's `latest_execution_payload_header` matches the execution node's genesis block.

The first commit also runs the merge-readiness/Capella-readiness checks prior to genesis. This has two effects:

- Give more information on the execution node's status and its readiness for genesis.
- Prevent the `el_offline` status from being set on `/eth/v1/node/syncing`, which previously caused the VC to complain loudly.

I would like to include this for the Holesky reboot. It would have caught the misconfig that doomed the first Holesky.

## Additional Info

- Geth doesn't serve payload bodies prior to genesis, which is why we use the legacy methods. I haven't checked with other ELs yet.
- Currently this is logging errors with _Capella_ genesis states generated by `ethereum-genesis-generator` because the `withdrawals_root` is not set correctly (it is 0x0). This is not a blocker for Holesky, as it starts from Bellatrix (Pari is investigating).

beacon_node/beacon_chain/src/errors.rs

@@ -146,6 +146,8 @@ pub enum BeaconChainError {
     BlockVariantLacksExecutionPayload(Hash256),
     ExecutionLayerErrorPayloadReconstruction(ExecutionBlockHash, Box<execution_layer::Error>),
     EngineGetCapabilititesFailed(Box<execution_layer::Error>),
+    ExecutionLayerGetBlockByNumberFailed(Box<execution_layer::Error>),
+    ExecutionLayerGetBlockByHashFailed(Box<execution_layer::Error>),
     BlockHashMissingFromExecutionLayer(ExecutionBlockHash),
     InconsistentPayloadReconstructed {
         slot: Slot,