SuperchainRegistry: improve the diff tools

[geoknee]

It should:

• be extended to compute and print a diff for op-geth, too (see this function https://github.com/ethereum-optimism/op-geth/blob/617815b4c1014fcf54cc482fd6ac54ba55237079/core/genesis.go#L259): Add genesis-diff tool #379
• Let’s also improve it to post a comment on the PR like the k8s diff bot and not count as a CI failure. The comment can come with warnings: “did a hardfork timestamp change? triple check to avoid chain splits!”
• Let’s also improve it to print a diff when a new chain is added, not just a modification to an existing chain.
• Let's update the registry readme (adding a new chain section). It should explain that a diff should be expected and the PR author should check to see it makes sense.
• It should handle changes in file name https://github.com/ethereum-optimism/superchain-registry/actions/runs/9663016365/job/26654171032?pr=320

---

https://www.notion.so/oplabs/Superchain-Registry-Failure-Modes-and-Recovery-Path-Analysis-f863f6e4e4bb49a5894f43d404319d8c?pvs=4#69687a82ff504460a3d070e550123d56