Add option to verify contract from Etherscan's ZKsync Explorer

[MexicanAce]

🌟 Feature Request

📝 Description

Add a Verify from Etherscan button on the Smart Contract Verification page, that checks if the contract is already verified at zksync.network and uses that public information to also verify the contract within the Block Explorer.

This button should only be displayed as an option if there's a corresponding Etherscan block explorer for the chain (e.g. Mainnet & Sepolia but not partner ZK chains)

🤔 Rationale

Sometimes there are smart contracts that are not verified on Block Explorer, but are verified on ZKsync's Etherscan explorer. It would be really great if there was an easy/quick option on the Smart Contract Verification page that would attempt to verify the contract based on the information from zksync.network

📋 Additional Context

Example contract that's verified on Etherscan's Explorer: https://era.zksync.network/address/0xE629B208046F7A33dE3A43931c9FE505A7Ac3d36#code

But unverified on our Block Explorer: https://explorer.zksync.io/contracts/verify?address=0xE629B208046F7A33dE3A43931c9FE505A7Ac3d36

[popzxc]

That would be a nice feature indeed (though I wonder if we can make it automatic), but first it has to be supported in the contract verifier.

Created a pre-requisite task: matter-labs/zksync-era#3390

This issue is blocked until then.