Implement skip_randao_verification and blinded block rewards API (#3540)

## Issue Addressed

https://github.com/ethereum/beacon-APIs/pull/222

## Proposed Changes

Update Lighthouse's randao verification API to match the `beacon-APIs` spec. We implemented the API before spec stabilisation, and it changed slightly in the course of review.

Rather than a flag `verify_randao` taking a boolean value, the new API uses a `skip_randao_verification` flag which takes no argument. The new spec also requires the randao reveal to be present and equal to the point-at-infinity when `skip_randao_verification` is set.

I've also updated the `POST /lighthouse/analysis/block_rewards` API to take blinded blocks as input, as the execution payload is irrelevant and we may want to assess blocks produced by builders.

## Additional Info

This is technically a breaking change, but seeing as I suspect I'm the only one using these parameters/APIs, I think we're OK to include this in a patch release.

consensus/types/src/beacon_block.rs

@@ -66,6 +66,8 @@ pub struct BeaconBlock<T: EthSpec, Payload: ExecPayload<T> = FullPayload<T>> {
     pub body: BeaconBlockBodyMerge<T, Payload>,
 }
 
+pub type BlindedBeaconBlock<E> = BeaconBlock<E, BlindedPayload<E>>;
+
 impl<T: EthSpec, Payload: ExecPayload<T>> SignedRoot for BeaconBlock<T, Payload> {}
 impl<'a, T: EthSpec, Payload: ExecPayload<T>> SignedRoot for BeaconBlockRef<'a, T, Payload> {}
 

consensus/types/src/lib.rs

@@ -99,7 +99,7 @@ pub use crate::attestation_duty::AttestationDuty;
 pub use crate::attester_slashing::AttesterSlashing;
 pub use crate::beacon_block::{
     BeaconBlock, BeaconBlockAltair, BeaconBlockBase, BeaconBlockMerge, BeaconBlockRef,
-    BeaconBlockRefMut,
+    BeaconBlockRefMut, BlindedBeaconBlock,
 };
 pub use crate::beacon_block_body::{
     BeaconBlockBody, BeaconBlockBodyAltair, BeaconBlockBodyBase, BeaconBlockBodyMerge,