Add new lotus-shed command for computing eth hash for a given mcid

[fridrik01]

Context
I needed a quick way to compute the eth hash for a given message cid so I could use that for constructing options to RPC calls like eth_getTransactionReceipt.

Test plan

Looked up a random message bafy2bzaceduvlffwumoq6j7rmx5evgsyl2fa3nh7oaqbzt7t4n3r75f2vqqpy on filfox and used that as an example:

./lotus-shed eth compute-eth-hash bafy2bzaceduvlffwumoq6j7rmx5evgsyl2fa3nh7oaqbzt7t4n3r75f2vqqpy
0xbc7c5ebdada305ea6922e5644fba5ecb283ce3f2f4cfe58a786eed744df70042

Confirmed that the returned eth hash is valid:

curl -s  http://localhost:1234/rpc/v1  -X POST -H "Content-Type: application/json" --data '{"method":"eth_getTransactionReceipt","params":["0xbc7c5ebdada305ea6922e5644fba5ecb283ce3f2f4cfe58a786eed744df70042"],"id":1,"jsonrpc":"2.0"}'|jq
{
  "jsonrpc": "2.0",
  "result": {
    "transactionHash": "0xbc7c5ebdada305ea6922e5644fba5ecb283ce3f2f4cfe58a786eed744df70042",
    "transactionIndex": "0x3f",
    "blockHash": "0x847a7fa6777a1fa7db9741a8e6d1a1eeb1590b0e1691021797f0add6f8bb0ac3",
    "blockNumber": "0x2b0c1d",
    "from": "0xb59ab49ef45d88fdeb6d955099d1a8d7cebb0d2b",
    "to": "0x66081f26cc780bc03fddb2839586f53f007b82b0",
    "root": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "status": "0x1",
    "contractAddress": null,
    "cumulativeGasUsed": "0x0",
    "gasUsed": "0x4b4366",
    "effectiveGasPrice": "0xaa2bef",
    "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
    "logs": [],
    "type": "0x2"
  },
  "id": 1
}