Add tests for src/gardenlinux/s3

[yeoldegrove]

What would you like to be added:

A similar test setup as for the OCI/registry classes would be nice to have in the S3 classes as well.
https://garagehq.deuxfleurs.fr/documentation/quick-start/ or deploying a small Minio instance https://min.io/docs/minio/container/index.html (or maybe even mocking minio calls https://pypi.org/project/pytest-minio-mock/) could be possible options.

Why is this needed:

Testing out new developments or bugs in the src/gardenlinux/s3 code before deploying them.

[ByteOtter]

Turns out that the minio library you mentioned does not support boto3 and from what I could gather doesnt work with the Bucket class implementation we have.
I found another module that would most likely work: https://github.com/getmoto/moto