Addition of a new billing-related domains

[mks-d]

This is a proposal for extending Iniz's capabilities to support metadata from the OpenMRS Billing Module:

BILLABLE_SERVICES that represents services that can be billed within the billing module with attributes such as the name, short name, concept, service type, service category, service prices, and service status, handling creation of billable services in the billing module e.g. Covid Vaccination Service that might be a billable service in a facility under the Vaccination Services, Ultra Sound Scanning Services under the Antenatal Services, Complete Blood Count that can be under Clinical Consultation Services etc.

CASH_POINTS which represents a locations such as OPD Clinic, ART Clinic within the OpenMRS billing module where bills can be created and paid

PAYMENT_MODES which are payment modes that represents different modes of payment (such as cash, mobile money or credit card) within the billing module which also allows for customisable attribute types, enabling users to define additional properties for each payment mode like the pricing of the different payments