Replace deprecated `aws-sdk-go-v2/feature/s3/manager` with `aws-sdk-go-v2/feature/s3/transfermanager`

[johha]

Package github.com/aws/aws-sdk-go-v2/feature/s3/manager is deprecated and should be replaced with github.com/aws/aws-sdk-go-v2/feature/s3/transfermanager.

Further details:
aws/aws-sdk-go-v2#3306

[johha]

transfermanager currently only has 0.x releases and looks pretty much like work in progress. There might be issues with RequestChecksumCalculation overrides. Should revisit this in a couple of months.