Etherlink/Floodgate: option to enable instant confirmations (benchmark)

Context

Closes L2-667.

V1 to benchmark instant confirmations. For now I manage to reach a satisfying state, i.e a state where we can quarry relevant data from preconfirmation stream etc.

We can incrementally improve it, but the current state is definitely usable and allows us to fetch reference data to compare with the different version of IC we will implement.

Testing

On rainbownet try:

floodgate run --relay-endpoint <relay-endpoint> --controller 0x0eb9bfa77d6cd145cdc0e3d6f902ee1464aeb5f62b02e38f111c9b60cd3adab5 --rpc-endpoint <rpc-endpoint> --ws-endpoint <preconfirm-stream-endpoint> --scenario erc20 --txs-per-salvo 1 --max-active-eoa 20 --benchmark-instant-confirmations <csv-file> --report 1

NB: The preconfirm stream endpoint should be launched with websocket enabled, otherwise won't work.