Add script to generate blsToExecutionChange for testnet validators.

[jimmygchen]

Add script to generate blsToExecutionChange for testnet validators to make withdrawal testing easier on local testnet. The script does the following:

• Set up the parameters required for generating blsToExecutionChange using staking-deposit-cli
• Runs staking-deposit-cli using docker and outputs the json to a local directory.
• Update local testnet to latest version to support Capella (copied from a Lighthouse branch)

To use this script, lighthouse and lcli needs to be built using this Lighthouse PR, so that we could use a given mnemonic to set up the genesis validators. See steps below.

Steps to test:

1. Check out the branch from sigp/lighthouse#3808 and build lighthouse and lcli: make && make install-lcli
2. Pull latest changes on this PR
3. Start testnet ./start_local_testnet.sh genesis.json (make sure geth & bootnode are installed and available on PATH)
4. Generate a blsToExecutionChange json:

# generate for validator index 0 & 1
./generate_bls_to_execution_change.sh 0 0,1 <eth1_address>

5. Submit the blsToExecutionChange json to beacon node:

curl -X 'POST' \\n  'http://localhost:8001/eth/v1/beacon/pool/bls_to_execution_changes' \\n  -H 'accept: */*' \\n  -H 'Content-Type: application/json' \\n  --data "@bls_to_execution_changes/bls_to_execution_change-<your_file_name>.json"

6. Wait until Capella fork (about 1 minute) and the BLS change messages are processed. If you're interested, look for this message in the beacon_node_<n>.log, but it should happen pretty quickly if you submitted the message after Capella fork, so feel free to skip checking this:

INFO Processed BLS to execution change

7. Confirm withdrawal_credentials are updated to 0x01:

curl -X GET "http://localhost:8001/eth/v1/beacon/states/head/validators/0" | jq .
{
  "execution_optimistic": false,
  "finalized": false,
  "data": {
    "index": "0",
    "balance": "32000001170",
    "status": "active_ongoing",
    "validator": {
      "pubkey": "0xa03c8f4fe1baf3b62ee1464778ae7a0bfe2fa3fe5baa454c4bfef35832b2378ecfe202a00cb05a34c2fc4c22bf6eff7c",
      "withdrawal_credentials": "0x01000000000000000000000049011adbcc3bc9c0307bb07f37dda1a1a9c69d2e",
      "effective_balance": "32000000000",
      "slashed": false,
      "activation_eligibility_epoch": "0",
      "activation_epoch": "0",
      "exit_epoch": "18446744073709551615",
      "withdrawable_epoch": "18446744073709551615"
    }
  }
}

NOTE: the local testnet is a copy from the Lighthouse repo, longer term we potentially want to unify them to reduce maintenance burden.

[jimmygchen]

@rickimoore I've copied all the latest Capella local testnet changes from @pawan's PR sigp/lighthouse#3807, there are a few important changes for starting up local testnet:

1. Clone and build geth and bootnode

https://github.com/ethereum/go-ethereum.git
git checkout v1.11.5
make all

2. Build lighthouse & lcli from this branch

# under the lighthouse directory
git fetch origin pull/3807/head:pr-3807
git checkout pr-3807
make lighthouse && make install-lcli

3. Start local testnet with this command instead (new genesis.json parameter)

./start_local_testnet.sh genesis.json

The local testnet works, however the generate BLS change script no longer works - I'll check with @pawan on how he's generating the keys. If generating the json file is important to you now, you may want to run local testnet with the older commit.

[jimmygchen]

For reviewer(s), this PR contains all local testnet scripts copied from sigp/lighthouse#3807 - I'm trying to keep it in sync (mostly) to the lighthouse repo keep it maintainable.

The only new change here is this file:
https://github.com/sigp/siren/pull/167/files#diff-8d8da66adb19d899688c9f2b897fca422fcc3355b7945e61e55853185213c4c3

[jimmygchen]

@rickimoore I can confirm blsToExecutionChange now works on the local testnet now! (thanks @pawanjay176)

I've updated the steps in the PR description.

[rickimoore]

gg