feat: allow task devs to supply custom addresses not in the superchain-registry

[blmalone]

This is a first version of an approach that allows task developers to supply custom addresses to the superchain-ops repo that do not exist in the superchain registry. This is useful for many reasons including upgrading devnets that do not exist in the superchain-registry.

[blmalone]

Instead of adding a new variable to the ChainInfo struct for .l2Chains, we should introduce a new TOML property called .l2ChainsLocal.

The .l2Chains and .l2ChainsLocal properties must not coexist in the same config.toml file.

• If .l2Chains is present, the task will perform onchain discovery as usual.
• If .l2ChainsLocal is present, the task will expect each L2 chain entry to include a file path pointing to a JSON file (matching the structure of SCR's addresses.json). The task will read all addresses from the file and skip onchain discovery.

This approach avoids breaking changes and keeps the config.toml API clean.

[blmalone]

Closing this in favor of a different PR. In rebase hell with this one.