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

dev/app/my-route/route.ts

@@ -1,11 +1,13 @@
 import configPromise from '@payload-config'
 import { getPayload } from 'payload'
+import { useBillingPlugin } from '../../../src/plugin'
 
 export const GET = async (request: Request) => {
   const payload = await getPayload({
     config: configPromise,
   })
 
+
   return Response.json({
     message: 'This is an example of a custom route.',
   })