Remove dependency on boto and only use S3 file system

[peteski22]

What's changing

• Remove the boto dependency
• Use s3fs as a replacement (presigned urls and listing files)
• Now requires some asynchronous calls
• Updated tests

Closes #473

How to test it

Steps to test the changes:

Additional notes for reviewers

Anything you'd like to add to help the reviewer understand the changes you're proposing.

I already...

• Tested the changes in a working environment to ensure they work as expected
• Added some tests for any new functionality
• Updated the documentation (both comments in code and product documentation under /docs)
• Checked if a (backend) DB migration step was required and included it if required