Ask for files on an upload page

Use this when the person has a file you can't pass yourself, or it's over 2 MB. Returns upload_url, a page where the person drops PDFs, and put_url, which takes one PDF as the request body for clients that make HTTP requests. Both work once, for 30 minutes. Each file becomes a document; find it with document_list or activity_list. With purpose "safe_import", for SAFEs signed elsewhere and their DocuSign certificates: after the drop the person checks what Binderwork read and imports them at review_url, and each then waits Unconfirmed in the register (captable_get with include register) for an officer. With purpose "captable_import", for a cap table export (Pulley's files, Carta's reports, an OCF package or a spreadsheet, with the agreements as PDFs): the spreadsheets, ZIPs and JSON files are kept in the archive, the PDFs become documents, and captable_prepare imports them with import.upload_id. With document_id, the one PDF dropped becomes that document's next version, under every link it has.