HDDS-10633. Support Content-MD5 header for checking object integrity when uploading object

[hevinhsu]

What changes were proposed in this pull request?

Add support for the Content-MD5 header to verify object integrity during object uploads.

Please describe your PR in detail:

• Validate the Content-MD5 header using pre-commit hooks before the key is committed.
• Add unit tests, integration tests, and end-to-end tests covering:
  • PUT object with Content-MD5
  • Multipart upload with Content-MD5
• Add no-argument constructors to KeyDataStreamOutput to simplify unit test setup.

What is the link to the Apache JIRA?

https://issues.apache.org/jira/browse/HDDS-10633

How was this patch tested?

https://github.com/hevinhsu/ozone/actions/runs/20842334193

[jojochuang]

Note:
https://docs.aws.amazon.com/AmazonS3/latest/API/API_Object.html

The ETag may or may not be an MD5 digest of the object data.

[hevinhsu]

Thanks @jojochuang for pointing this out.

I agree that the final ETag may not always be an MD5 (especially for multipart or encrypted objects). However, this patch focuses on in-transit integrity checking via the Content-MD5 header.

During the upload, S3G calculates the MD5 of the incoming data stream to verify it against the client-provided Content-MD5. This verification happens before the object is committed. The document you shared refers to the ETag's behavior after the commit, which is independent of the Content-MD5 validation logic at the ingestion stage. Therefore, the ETag's final format does not affect this check.