Enable spinning a non-clique devnet L1

[norswap]

Clique chains do not mark their blocks as finalized, and therefore do not enable testing of L2s without the --allow-non-finalized flag on the proposer.

It also seem generally useful to help people to very simply spin a Ethereum-like chain.

Priority for this is pretty low however, --allow-non-finalized is ultimately just a timing detail, and a local devnet will not revert blocks.

Two sources to look at for the setup:

• https://github.com/ayazabbas/devnet-ansible/tree/main
• https://github.com/OffchainLabs/eth-pos-devnet