L2: Improve Privileged Txs UX experience

[mationorato]

I discussed this with @ilitteri and @jrchatruc, and we agreed that we should add an address indexed L1From (the name can be adjusted) to the event PrivilegedTxSent on crates/l2/contracts/src/l1/interfaces/ICommonBridge.sol so that wallets can track their own privileged transactions for UX purposes.

We also agreed that this should be the only indexed parameter, unless someone can provide a strong reason to keep from, to, or id indexed.

L1From should be set to msg.sender when emitted.

Originally posted by @mationorato in #3365 (comment)