Feature: Support self-hosted and local S3 instances

[AntoineJT]

Hello, thank you for your work!

Your project has been useful to me for presenting data to non-technical users, using a local development LocalStack server as an S3 instance.

To achieve this goal, I tinkered a bit with your tool in local.

I figured out it could be useful to other people, so I made the tinkering a real thing by cleaning up my changes and opening this pull request.

Feature

• Allow users to use your application with self-hosted or local S3 instances, by allowing endpoint overriding
  • Add an AWS_ENDPOINT_OVERRIDE environment variable for overriding endpoint
  • Add an AWS_REQUEST_SCHEME environment variable for allowing to choose between http and https
• Add support for path-style URLs (old URLs)
  • Add a FORCE_PATH_STYLE environment variable for enforcing usage of old path-style URLs instead of virtual-hosted-style URLs

[AntoineJT]

@tlinhart Hi, it's been 21 days since I opened this PR

Do you want me to change some things? (besides rebasing)

Are you accepting new features, or is this app in maintenance-only?

[tlinhart]

Hi @AntoineJT and sorry for the radio silence. I appreciate your work and plan to go through it. I was hoping to find some spare time but didn't get to it yet. There are definitely a couple of things I'd like to discuss and possibly change, but overall I think it's a useful feature. Just need more time to delve into it.

[jaysoni-india]

this changes looks pretty useful for connecting to local MinIO sever (alternative to S3 for on-premises system)