Incorrect Mining Reward for Genesis Block

[talevy]

Describe the bug
I believe the miningReward calculation for the genesis block (height = 0) is possibly incorrect

https://github.com/coinbase/rosetta-ethereum/blob/79a9b97d0a3ed08ae151a3f313aa57b88dd128a4/ethereum/client.go#L971-L976

To Reproduce

curl -XPOST --head localhost:8080/block -d'{                                                                                                                                                            
  "network_identifier": {
    "blockchain": "Ethereum",
    "network": "Mainnet"
  },
  "block_identifier": {
    "index": 0
  }
}'

Expected behavior

The mining reward for the genesis block is 5 ETH. that is according to https://etherscan.io/block/0

Additional context

If this is expected, then that is fine by me too! just checking here because etherscan and rosetta mismatch here. thanks!

[thepabloaguilar]

@shrimalmadhur I'd like to work on this one!