Switch backend to ethereum-api

[pedrouid]

Balance Indexer backend currently only supports Mainnet and this could be improved by using the ethereum-api which will support all chains supported by Blockscout.

Additionally Balance Indexer should fork ethereum-api and add aggregate price feeds from a different source like coinmarketcap for more accurate price

[pedrouid]

cc @tomjohnburton

[pedrouid]

ethereum-api repo: https://github.com/pedrouid/ethereum-api

[tomjohnburton]

interesting project. I'll take a look!