RFC: Banking integration

[JannikZed]

We should add generic support for bank accounts and bank transactions. We already have it specialized on payments, but we would need to add more features for traditional bank accounts.
This would allow us for example to match bank transactions with open invoices / pre-payment processes. A tenant config could include for example a logic, that marks orders automatically as ready to fulfill when fully paid.
Bank transactions can be pulled from Zoho Books
or way better with an adaptor from for example https://ob.nordigen.com/overview/. This includes the creating of a webpage, where users can connect their banks to schemabase and update their connection.