Scripts to run proveOnChain through a Gnosis Safe

[auryn-macmillan]

There are significant gas costs involved with submitting proofs on-chain on L2, which currently means trusting significant amounts of ETH to an EOA.

The optimal solution to this is to reduce the proving costs to a point where securing them with an EOA is acceptable. In the interim, however, it could be valuable for us to make a version of the proveOnChain script that uses a Gnosis Safe for each call to MACI.

I think it's reasonable to make an assumption that the script would require the signers to be running synchronously, perhaps one as the coordinator and some threshold of others running a co-signer script that watched the safe transaction service and only approves the appropriate transactions to the MACI contract.