FEATURE: Add TUS file upload

[daniellienert]

This feature adds file upload via TUS (https://tus.io/) protocol. This brings the following advantages:

• Files are split into chunks, which makes uploading of files of any size possible (independent from the servers max_upload limit)
• Uploads of the chunks can be resumed, which makes uploads of large files stable even with shaky connections

To discuss:

• Should graphQL upload be removed -> will stay

https://user-images.githubusercontent.com/642226/142685892-42b7907a-3a36-4d32-bbec-8f68d32aa99d.mov

Resolves: #61