feat(s3): Introduce S3 compatibility

[SirBerg]

This PR introduces S3 storage backend support and the appropritate configuration options for it. Although I've verified it works it should be treated as an Alpha release and not stable.

How to test

Download the branch, run docker-compose up -d and verify that your storage_type in config.toml is set to "s3" and that you have set appropriate values in [storage.s3] (depending on how you've configured minio).
This is something sensible that worked for the current dev setup:

[storage.s3]
access_key_id = "iglu"
secret_access_key = "iglu_dev_pw" 
bucket = "iglu"
endpoint = "http://localhost:9000"

After you've verified all that, run bun cache::dev and push to the cache like you normaly would, everything should work transparently to the cachix client.

[Svenum]

lgtm

GREAT WORK 👍