proxyd: Use canned response for eth_accounts

[mslipper]

We never want to expose Geth's accounts to the public internet, so proxyd will now return [] for eth_accounts RPC calls without hitting the backend.

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Latest commit: 6ea4e8c

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@eth-optimism/proxyd	Patch

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[optimisticben]

lmtm

[Inphi]

Looks good.

Super nit incoming:
However, this makes proxyd even more specific to our infrastructure. A couple folks have expressed interest into using proxyd for generic JSON-RPC routing. I dunno if anyone else deploys proxyd for other networks, but this would be a surprising change in behavior.

[mergify]

This PR has been added to the merge queue, and will be merged soon.

[mergify]

This PR is next in line to be merged, and will be merged as soon as checks pass.

[optimisticben]

Super nit incoming: However, this makes proxyd even more specific to our infrastructure. A couple folks have expressed interest into using proxyd for generic JSON-RPC routing. I dunno if anyone else deploys proxyd for other networks, but this would be a surprising change in behavior.

That's a good point. This should be behind a feature flag tbh.