feat: Add support for provider-level configuration in billing plugin

- Introduce `onConfig` callback for payment providers
- Add dynamic endpoint registration for Mollie webhook handling
- Remove unused provider-specific configurations from plugin types
- Update initialization to include provider-level configurations

src/providers/types.ts

@@ -1,10 +1,12 @@
 import type { Payment } from '@/plugin/types/payments'
-import type { Payload } from 'payload'
+import type { Config, Payload } from 'payload'
+import type { BillingPluginConfig } from '@/plugin/config'
 
 export type InitPayment = (payload: Payload, payment: Partial<Payment>) => Promise<Partial<Payment>>
 
 export type PaymentProvider = {
   key: string
-  onInit: (payload: Payload) => Promise<void> | void
+  onConfig?: (config: Config, pluginConfig: BillingPluginConfig) => void
+  onInit?: (payload: Payload) => Promise<void> | void
   initPayment: InitPayment
 }