Improve errors related to object storage authentication. #52
Description
New error variant on ObjectStorageError is needed to correctly display authentication failure and let users know if credentials provided are wrong.
Currently on authentication failure, ObjectStorage::check returns Unhandled Error: Error. This method for S3 is implemented by call to head_bucket which returns aws_sdk_s3::types::SdkError<HeadBucketError> but is mapped to unhandled error variant.