[POC] Finalize bridge transactions mechanism

[thomas-nguy]

The finalize method needs to called after a bridge transfer in order to effectively receive tokens on l1 or l2.

While this is supported by the SDK, this is not supported by the UI
We assume that on era mainnet, matter-labs team is subsidizing the bridge so that it is called without user interactions.

In our case, we can think about two options

1. Ask user to trigger finalize themselves their transactions on the bridge UI. after the block has been relayed to l1 or l2
2. Add an additional cost on the bridge transfer, and create a "process" that will finalize on the behalf of the user. We need to make sure that this process will get effectively paid for its work.

[thomas-nguy]

It seems that matter-labs will open source soon their "Withdrawal finalizer - A service to automatically finalize L2>L1 withdrawals"