Replay attack prevention

[SebastienGllmt]

We need to provide replay protection by making that the witnesses for a L2 transaction cannot be reused on the L1 (or vice-versa)

[L-as]

Commands include the network they apply on, so this is in some sense a "built-in" feature already. We don't use it right now however since tooling doesn't support signing such commands easily.

[L-as]

We need to do this.