upload_session/start

[upload_session/start](https://www.dropbox.com/developers/documentation/http/documentation#files-upload_session-start) scope: `files.content.write` Upload sessions allow you to upload a single file in one or more requests, for example where the size of the file is greater than 150 MB. This call starts a new upload session with the given data. You can then use `upload_session/append:2` to add more data and `upload_session/finish` to save all the data to a file in Dropbox. A single request s...