Create a new attachment

Endpoint to create a new attachment. This endpoint allows the creation of a new attachment with the following fields: - `file`: The file being attached (required). - `transactions`: List of related transactions, see more in /api/v1/accounting/transactions/. - `company`: The company associated with the attachment, see more in /api/v1/companies/. - `attachment_type`: Type of the attachment, available types: invoice, receipt. - `amount`: Amount related to the attachment. - `amount_exchanged`: Exchanged amount in a different currency. - `attachment_number`: Unique number for the attachment. - `brand_name`: Brand name associated with the attachment. - `currency`: Currency of the amount, default is "EUR". - `currency_exchanged`: Exchanged currency, default is "EUR". - `description`: Description of the attachment. - `supplier_country`: Country of the supplier, available choices are: [ [ "DE", "Germany" ], [ "INSIDE_EU", "Inside EU" ], [ "OUTSIDE_EU", "Outside EU" ] ]. First value in the array is the db-understandable code, second is the representation. - `value_date`: Date of the value. - `vat_sum_amount`: VAT sum amount. - `vat_sum_amount_exchanged`: Exchanged VAT sum amount. - `vat_rate`: VAT rate, see more in /api/v1/choices/vat-percents. - `sale_type`: Type of sale, see more in /api/v1/choices/sale-types/. - `additional_metadata`: Additional metadata for the attachment. All fields except `file` are optional.