Attach an uploaded file to a work item

Turns bytes you have already uploaded into an attachment on the work item named in the path, and returns the file in the detail view. upload_id is the only key this accepts: create a ticket with POST work-items/{work_item}/uploads, PUT the raw bytes to its upload_url, then send its id here. Everything about the file (its name, its size, its media type, its collection and its storage location) is read off the ticket and off the bytes that actually arrived, so file_name, mime_type, byte_size, collection and disk are all a 422. The ticket must have been created for this work item, by this API token, and must not have expired or been registered already; each of those is a specific 409 or 422 naming the cause. The server re-hashes the stored bytes and compares them with what it received before creating anything. This works exactly like an upload in plnnrly, so thumbnails and notifications follow identically. Attaching requires project_management::manage_work_items, the same permission plnnrly checks. Idempotency-Key is required: a lost 201 retried without one would report a failure for a create that succeeded. There is no Location header (a file has no item URL of its own), and no PATCH or DELETE on a file; remove one in plnnrly.