Generate Arbitrum Bridge Proof

[efecarranza]

Changelog

Add command to generate Arbitrum burn proofs.

[sakulstra]

@efecarranza sorry missed this one before, could you add some context here on why/what for this is needed?
It's a quite huge dependency as it seems like if forces us to use ethers OffchainLabs/arbitrum-sdk#321

If it's useful for aave ofc, we'll consider adding it, but right now it's not clear to me, plz elaborate.

[efecarranza]

@sakulstra hey Lukas, sorry I had missed this before.
in order to generate the proof to exit the bridge, unlike polygon which offers an API endpoint, arbitrum only offers to do it via SDK (same as optimism). therefore, i decided to make some utility to abstract some of this away and make this easier for anybody doing a bridge from arbitrum to mainnet.