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.

beacon_node/http_api/src/block_rewards.rs

@@ -4,7 +4,7 @@ use lru::LruCache;
 use slog::{debug, warn, Logger};
 use state_processing::BlockReplayer;
 use std::sync::Arc;
-use types::BeaconBlock;
+use types::BlindedBeaconBlock;
 use warp_utils::reject::{
     beacon_chain_error, beacon_state_error, custom_bad_request, custom_server_error,
 };
@@ -96,7 +96,7 @@ pub fn get_block_rewards<T: BeaconChainTypes>(
 
 /// Compute block rewards for blocks passed in as input.
 pub fn compute_block_rewards<T: BeaconChainTypes>(
-    blocks: Vec<BeaconBlock<T::EthSpec>>,
+    blocks: Vec<BlindedBeaconBlock<T::EthSpec>>,
     chain: Arc<BeaconChain<T>>,
     log: Logger,
 ) -> Result<Vec<BlockReward>, warp::Rejection> {