Enables the Global Payroll product on a legal entity so that GP employees can be created against it.

Performs three idempotent steps:

• Adds the Global Payroll product to the company.
• Flips global_payroll_enabled on the legal entity's settings.
• Ensures a Global Payroll pricing plan exists for the legal entity's country.

This endpoint is only available in Sandbox, otherwise it will respond with a 404.