Download url

Adding a new method to the File class that will grab the short lived download url. 
Adjusting the old `File#download` method to use this instead. 

Motivation for this change: 
Assuming that a user is interacting with the gem through a browser. 

Most of the time we do not want to download the file, and then send it to the client since if the file is large we will have to download the full file before sending it and that could take quite some time which will slow down the requests. Instead, we can redirect to the download url and let the user download it directly.