Modify EVM node configuration to support arbitrary L2s

What

This MR changes the configuration of the EVM node. Notably, it introduces the concept of chain_configuration that will contain all the information particular to each particular chain when we have a canonical rollup with multiple chains, the most notable of which is the chain_id.

This brings some modifications from the rafoo@etherlink_duplication branch to master, but it does not include modifications outside the EVM Node configuration except where it is necessary to compile.

Why

Essential for having multichain rollups.

How

The first commit establishes the chain_id type.

The second commit creates the l2_chain type, used to indicate the configuration of an individual l2_chain. We then add the l2_chains field to experimental features, an optional list of such configurations.

The third commit sets the l2_chains when given the --network parameter.

The fourth commit updates the Changelog.