HDDS-15182. [STS] Remove latent extra read on CopyObject api - make CopyPart work similarly

[fmorg-git]

Please describe your PR in detail:

• In STS, CopyObject requires s3:GetObject action on source and s3:PutObject action on destination in order to successfully invoke the api. In the latent S3 implementation, the code was doing an additional read on the destination object to get the eTag and modificationTime when the file was created. This is problematic, because AWS doesn't require s3:GetObject action on the destination file, so this extra read was causing STS smoke tests to fail.

In order to address, don't do the extra read (which will help performance as well) and instead make the commit key call return the modification time in the response and use that. Furthermore, the code already knows what the md5Hash/eTag is, so there is no need to read the destination object.

For consistency, make uploadPartCopy similarly return the modification time as well.

This PR depends on #10197.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-15182

How was this patch tested?

unit tests, smoke tests