Orderbook chain-commitment: simple `OP_RETURN` flow

I looked more on the `submitToMainstay` flow.

For now, I think we can do something far simpler for the first releases.

Every 24 hours, take all the `orderId` from the latest 24 hours.

Concatenate them in a single data byte vector sorted by alphanumeric order.

Hash the vector with an hashing function (e.g SHA256 or SipHash).

Commit the 32-byte hash output in an `OP_RETURN` bitcoin tx output scriptpubkey.

Broadcast and confirm the bitcoin tx.