Spike: Define API Design For Unified Purchase Flow

Purpose

This spike aims to define the API design for the unified purchase flow.

Objective

Define the API design for the remaining subscription actions in the unified purchase flow.

• Upgrade Premium to Ultimate
• Renew

This will help us implement the unified purchase flow in such a way that adding new product offerings will require a less hands on approach.

Result

• API design is defined for unified purchase flow
• High level task breakdown is updated with any additional work
• Level of effort is estimated and added to LoE in #11461 (closed)