Add support for S3 as source for bundler

Describe the problem as clearly as you can

Rubygems supports AWS S3 (hopefully also other object stores) as source for gems. See https://guides.rubygems.org/using-s3-source/

However, bundler does not support the same feature.
It should support also AWS S3 (and hopfeully other object stores) as source.

My Gemfile should be able to look like this:

source "https://rubygems.org"

source 's3://my_bucket' do
  gem 'my_secret_gem'
end

Did you try upgrading rubygems & bundler?

Sure. This is related to a old/closed issue: #3382

Post steps to reproduce the problem

N/A

Which command did you run?

N/A

What were you expecting to happen?

I think this repo from like 10 year ago describe very well what I expect to happen https://github.com/tmaier/docker-s3-gemserver
I should be able to define a s3 bucket as source for my private gems. I should be able to provide the necessarz secrets via env variables, so that I can access a private bucket.

What happened instead?

S3 is just partially supported. By rubygems, but not bundler

If not included with the output of your command, run bundle env and paste the output below

Start with Bundler's handling of the Gemfile source form shown in the issue, then review the Rubygems S3 source guide and the prior issue #3382. Done means Bundler can resolve private gems from an S3 bucket, with credentials supplied through environment variables, while preserving the existing rubygems.org source behavior.