Change payment processing to always use ephemeral accounts. Even for contract payments.

MERGE REQUEST

Overview

This MR changes the payment processing code to always deposit the money transferred by a contract payment in an EA. That way we can treat every RPC as if it was funded by an EA and refund renters on contract paid RPCs.

Checklist

Review and complete the checklist to ensure that the MR is complete before assigned to an approver.

• All new methods or updated methods have clear docstrings
• Testing added or updated for new methods
• Any new packages are added to Makefile and .gitlab-ci.yml
• API documentation updated for API updates
• Module README.md updated for changes to workflow
• Issue added to Sia-UI repo for new supporting features
• Changelog File Created