Direct upload to remote s3

[yigitsoy]

This PR attempts to address the issue described in #89 where the files can be uploaded to a remote s3 bucket directly without local storage.

@np-8 I tried to keep the changes only on python side. I would be happy if you could see if there are any places that can be improved.

[fohrloop]

Hi @yigitsoy ! Thanks for the PR and sorry for the delay! Did you have time to test this with S3? Adding automated test would not hurt, and I guess the test should just check if the send HTTP requests look correct

[yigitsoy]

Hi @np-8 Thanks for the feedback. I have been using this version to upload to S3 since then. I will try to some tests to make sure that it works in general.

[mapix]

@yigitsoy
Great job, I will assist you in the follow-up development and test this feature together.

[samkikibaker]

Very keen to see this as a feature so giving this a bump

[addionisio]

Would also love to see this feature. Has anyone had issues using this forked version with a Dash app that has a requests_pathname_prefix defined? When I have it defined, the s3 uploader fails to upload but when I remove it, the uploader works perfectly fine.