Improved support for MinIO

[AppleKid7]

There is some support for MinIO currently, but the credentials are hard-coded:

https://github.com/golemcloud/golem/blob/main/golem-worker-executor-base/src/storage/blob/s3.rs#L54

I started to work on parametrizing the credentials but ran into some issues building Golem and running the tests on my usual Windows/WSL setup. I'll continue to work on this once I have set up an actual Linux machine.