feat(earn): prepare transactions and use on confirmation screen

[MuckT]

Description

Handles the preparation of all earn transactions via a shared hook that's used on both EarnEnterAmount.tsx & EarnConfirmationScreen.tsx.

Test plan

• [x] Tested locally on iOS
• [ ] Tested locally on Andorid
• [ ] Unit Tests updated

Related issues

• Part of ACT-1389

Backwards compatibility

Yes

Network scalability

N/A