kovan: add eth gateway

[tynes]

No description provided.

[snario]

From the perspective of an external reviewer / someone just beginning to familiarize myself with with the ways that these kind of values get generated, it might be helpful to include some context as to why it was missed when the README was most recently modified on this repository anyway. From a quick search I did notice that this seems likely related to ethereum-optimism/contracts#245 (comment) — the code isn't verified on Etherscan yet.

Separately, from a brief glance at kovan/2.json it seems 0x6647d5bd9eb9425838bb89f76a166228b95671a3 is not present. Should it be?

[tynes]

The reason as to why it was not included in this file already was because it was deployed after the other contracts were deployed. I'd like to move to a world where there is a nice markdown table that includes the addresses with a link embedded that points to etherscan. Also we should consider having the source of truth be in the contracts repo after ethereum-optimism/contracts#249 is completed

[tynes]

Separately, from a brief glance at kovan/2.json it seems 0x6647d5bd9eb9425838bb89f76a166228b95671a3 is not present. Should it be?

That file has the L2 genesis state and this particular contract is deployed on L1