Allow DELEGATECALL as a UI option

[adhusson]

Overview

Being able to DELEGATECALL from the UI would be very useful.

Txbuilder is not great if you want to automate building multi-actions and also having each signer verify them (the tenderly simulation only gets you so far). You can initiate delegatecalls from safe-cli but there is no ledger support which rules it out immediately.

Adding easy delegatecalls enables the pattern "write a smart contract, verify it, delegatecall its run() function" which unlocks a lot of ways to verify the onchain effects of that contract.

Requirements

Add a checkbox (with a clear warning) to initiate delegatecalls from the UI.