Integration of era1 files into Nimbus EL

[Kim De Mey]

This issue is related / similar to #2147

The difference being that here we would have the era1 files as data backend, instead of the Portal network.

Eventually, the EL could decide to access the local database, era1 files and/or Portal network for the history content older than x.

[Mamy Ratsimbazafy]

Note that TheGraph and Geth are using era files here:

• ethereum/go-ethereum#26621
• https://ethresear.ch/t/using-the-graph-to-preserve-historical-data-and-enable-eip-4444/17318

[Kim De Mey]

Note that TheGraph and Geth are using era files here:

Thanks, was not aware of TheGraph, I'll read up on that.

I am aware of go-ethereum as we implemented era1 here in nimbus-eth1 to be able to give feedback before that PR went in: https://github.com/status-im/nimbus-eth1/blob/master/fluffy/eth_data/era1.nim