feat: Add Mollie payment provider support

- Introduce `mollieProvider` for handling Mollie payments
- Add configurable payment hooks for initialization and processing
- Implement `initPayment` logic to create Mollie payments and update metadata
- Include types for Mollie integration in payments and refunds
- Update `package.json` to include `@mollie/api-client` dependency
- Refactor existing payment-related types into modular files for better maintainability

src/collections/hooks.ts

@@ -0,0 +1,11 @@
+import type { Payment } from '@/plugin/types'
+import type { Payload } from 'payload'
+import { useBillingPlugin } from '@/plugin'
+
+export const initProviderPayment = (payload: Payload, payment: Partial<Payment>) => {
+  const billing = useBillingPlugin(payload)
+  if (!payment.provider || !billing.providerConfig[payment.provider]) {
+    throw new Error(`Provider ${payment.provider} not found.`)
+  }
+  return billing.providerConfig[payment.provider].initPayment(payload, payment)
+}