Anyone can upload a document to any ticket. However, an administrator still needs to add an expediture to the ticket, which isn't great.
Tracker should allow users to add amount listed at the document they're uploading within the upload form.
Student is expected to send a patch for wikimedia-cz/tracker repository, hosted at Wikimedia Gerrit. When claiming task on GCI website, student should claim a respective Phabricator task as well.