Add Sales Invoice Upload, Revenue Tracking

Currently, GetInvoice allows users to upload expense invoices, automatically scan expenses, and visualize these in the portal with graphs and overviews. We would like to extend this functionality to also support uploading sales invoices. This will allow users to track their revenue (sales) in the same portal, with clear visualizations and reporting, similar to the existing expense tracking.

Other advantage is that this way (both expenses and sales invoices) should allow accountants to view, download, and export documents for accounting purposes in 1 place.