Base price per watt range in Users API

The Users API now includes two fields, base_price_per_watt_max and base_price_per_watt_min, for managing an allowable base price-per-watt (PPW) range, adding guardrails for users who interact with pricing, and protecting margins on sold projects. The fields can be written using the Update User or Create User APIs, and read using the Retrieve User API. When a design's base PPW is changed to conflict with the PPW rule for the project's assigned user, a warning will appear in app for that user and anyone with access to the project.