Support for goerli testnet

[pipermerriam]

Depends on:

• Add support for "clique" based consensus py-evm#1457
• Support for custom genesis via EIP1085 py-evm#1299

What should be done.

We should add support for the new clique based POA testnet

https://github.com/goerli/testnet

[lithp]

Related, support for clique: ethereum/py-evm#1457

[veox]

For ref, @cburgdorf implemented the bulk of this in py-evm, in PR ethereum/py-evm#1855.

From the related issue:

(...) it won't be able to spin up a Py-EVM based node as an actual Görli validator but it's possible to sync the Görli network just fine.

There's a placeholder/draft PR for Goerli/Clique here, at PR #1196 (which should at least mention this issue ;)).

[veox]

ethereum/py-evm#1457 is closed. Technically, there's Clique now, but there are still issues with syncing:

• likely consensus failure (quite probably not Goerli-specific), Consensus failure (full-sync, all chains) on contract create/destruct within same block #1478;
• can't handshake with Nethermind (not Goerli-specific, just very visible), no issue yet;
• some trouble with peer discovery (not sure if Goerli-specific), no issue yet.