Add sync_committee_rewards

[kevinbogner]

Reference: #260 (review)

/eth/v1/beacon/rewards/sync_committee/{block_id}

{
  "execution_optimistic": false,
  "finalized": false,
  "data": [
    {
      "validator_index": "0",
      "reward": "2000"
    }
  ]
}

[dapplion]

@michaelsproul how do you plan to fulfill this API? AFAIK we don't have that information available after block processing since the rewards are "merged" into the balances array

[michaelsproul]

@dapplion I'm intending to replay blocks. For sync aggregates it's just a matter of loading the pre-state, and calculating the rewards based on the bits set in the sync aggregate

[michaelsproul]

Looking good! Almost ready to go I think

[michaelsproul]

LGTM, I'm happy to merge.

[ensi321]

Just renamed types/sync_committee_rewards.yaml to rewards.yaml. It will be merged with types/rewards.yaml in the other PR

[rolfyone]

LGTM, I think post will be better once you get into it, so thanks for persisting!

[rolfyone]

LGTM