Add support for gasless transactions to Transact Step

[efstajas]

We are thinking about sponsoring some transactions on FVM entirely since gas cost is so low. When sponsoring a non-anonymous transaction, we still need to prompt the user to sign a message in their wallet, but not execute a transaction.

For this, we should add a new mode to the new Transact Step that shows transaction's gas as "Paid for by Drips", and prompts the user to "Sign in wallet" instead of sending a transaction.

[brandonhaslegs]

Here's a little badge I worked on for this https://www.figma.com/design/vyI7f996JF8zwhnXwAwXdC/%F0%9F%92%A7-Drips?node-id=10962-24964&t=WT2WT5qP7eTjgEcw-4

Also thought of the badge saying "PAID BY DRIPS"

[efstajas]

@brandonhaslegs make version without real gas estimation, just gas icon, $0.00 and "Gas covered by DRIPS"

[brandonhaslegs]