45 create billing core tables (#4096)

* Add self billing feature flag

* Add two core tables for billing

* Remove useless imports

* Remove graphql decorators

* Rename subscriptionProduct table

packages/twenty-server/src/core/billing/billing.module.ts

@@ -0,0 +1,6 @@
+import { Module } from '@nestjs/common';
+
+@Module({
+  imports: [],
+})
+export class BillingModule {}