Create a new user in the enterprise. At least one of 'phone' or 'email' must be provided. The user will be created with an 'employee' role by default. Use the 'allocations' field to assign the user to subsidiaries and cost centers. If no cost centers are specified for a subsidiary, the user will be automatically assigned to ALL cost centers of that subsidiary. Users created without allocations will have is_active=false and can be activated later by adding allocations. Note: subsidiary_id, user_manager_id, and cost center ids can be provided as either UUID or internal_id.