refactor(l2): l1_watcher make deposits unique

[fborello-lambda]

Motivation

We need a way to identify deposit. In order to do it, we can use a "depositId" that works as a counter. It is being incremented every time a deposit event is emitted.

We've been starting the l1_watcher from block 0. Fetching logs from block 0 will throw errors if asking light_nodes and it's wasteful. We will need a more robust way to keep track of it, for now, we should start from the first block in which the CommonBridge was deployed.

Description

• [CommonBridge] Use the depositId to construct the deposit_hash (keccak(to || value || depositId))
• [L1Watcher] Use the depositId from the logs to avoid duplicating the mint transaction. And use it as the mint transaction's nonce. In this way, the [Committer] can create the StateDiff to send the commit transaction to the OnChainProposer.
• Add useful Makefile targets.
• Add simple command to fetch the depositId.
• Start from the block in which the CommonBridge was deployed.

Closes #1191