Creates a new bank transaction record with the specified parameters.

Bank transactions can be created to track money movements in and out of accounts.
New transactions are created with 'pending' status and 'manual' source by default.
They go through a reconciliation process to match them with expected accounting movements.

When creating a transaction, you must specify the amount, description, date,
and nature (payin/payout).

This endpoint uses the BankTransactions::ImportService to process the transaction.