Add multisig broadcaster type

[mslipper]

We need a way to manage upgrades for chains that use a multisig like OP Mainnet. To do this, we'll need a special broadcaster type for multisig transactions. This broadcaster will aggregate broadcasts, then output a Gnosis SAFE transaction JSON for future execution.

As part of this, we can also add a parameter to the intent to transfer ownership over the L1 system to an address of the user's choice.

DoD:

• Add support for final address transfer step.
• Implement new broadcaster type
• Integrate new broadcaster type

[tynes]

We used to have some Go types that made it easy to build Safe compatible JSON files. They were removed in https://github.com/ethereum-optimism/optimism/pull/11021, you might be able to find them useful for this