Indexes the new validator withdrawal objects (from Shanghai/Capella fork: https://eips.ethereum.org/EIPS/eip-4895)
- new table `eth.withdrawal_cids`
- new column `withdrawals_root` in `eth.header_cids`
- add unit tests
- use new external stack repo in CI/CT job (cerc-io/fixturenet-eth-stacks#14)
Reviewed-on: #25
* refactor packages, flags, subscriptions
* DRY refactor builder tests
* use mockgen to generate mocks
* update README
* MODE=statediff no longer needed for unit tests
* simplify func names, clean up metrics
* move write params to service field
* sql indexer: confirm quit after ipld cache reset
prevents negative waitgroup panic
* don't let TotalDifficulty become nil
* use forked plugeth, plugeth-utils for now
