Provide Kurtosis config for an Erigon private dev network

[sealer3]

Kurtosis (via https://github.com/ethpandaops/ethereum-package) is the currently accepted way of running private Ethereum dev networks, and currently the only non-deprecated way to run one in geth.

Our current docs list a way to launch the official Erigon dev network, which unfortunately is getting dated and only supports an older version of the EVM. I think it's fine for our internal tests, but if you do any kind of Ethereum development, you'll want to have a modern version of the EVM.

I think we should

• Migrate these devnet setup docs to an earlier section than Sourcify
• Replace the Erigon devnet, which doesn't seem to be getting much support anyway, with a Kurtosis (Ethereum Package) configuration