feat(O3-5372): add billing configuration to core reference application

[Chennamma-Hotkar]

Overview

Fix Version: RefApp 3.7.0
Adds the foundational billing Iniz configuration to the core reference application, enabling the billing module to function out of the box.

Changes

Created 3 new configuration folders:

billableservices/billableServices.csv

• OPD Consultation
• Acetaminophen (drug)
• Amoxicillin (drug)

cashpoints/cashPoints.csv

• OPD Cash Point

paymentmodes/paymentModes.csv

• Cash
• Bank Transfer

Why

Previously, billing required manual UI setup after deployment. These Iniz files allow the billing module to be fully configured declaratively, consistent with the OpenMRS initializer-first configuration approach.

Dependency

Requires the backend fix from openmrs-module-billing#[114]

Related PRs (merge in order)

1. feat(O3-5372): auto-generate bill from medication orders via BillableService fallback openmrs-module-billing#114 (backend - merge first)
2. feat(O3-5372): add billing configuration to core reference application #12 (core config)
3. feat(O3-5372): add drug billable services to demo configuration openmrs-content-referenceapplication-demo#61 (demo config)