s3store: Try out Minio SDK

[Acconut]

Currently the s3store uses the official AWS Go SDK. We are continuously seeing high CPU usages with this. It is quite likley that this usage comes from the network communication with S3 and/or the writing off the temporary files.

To rule out that the AWS Go SDK itself provides an overhead, we might try switching to the Minio SDK (https://docs.min.io/docs/golang-client-api-reference) in a separate test release for a benchmark session.

In addition, I want to investigate whether it is possible/sensible to avoid writing to the temporary file and instead only keep one part buffered in memory.