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.