feat: Secret Delay

[fabianschu]

User Story
As a monetary delegate, I want proposed transactions to remain secret until they are executable, so that I don't create adverse arbitrage opportunities.

Status Quo

• in the original Zodiac Delay module from which this repo is forked when a transaction is proposed, the module creates and stores its hash on-chain
• when the transaction becomes executable (because the cooldown is over) anyone can execute the transaction using the same (publicly available) transaction parameters from when the the transaction had been proposed
• before the transaction is executed, the module would hash the transaction and compare it against the hashes that had been saved before

AC

• in addition to the transparent way of proposing it is possible to propose a transaction secretly