Add GetObjectRetention satellite endpoint (object retention)

[amwolff]

Goal

This issue is to make meaningful progress on Object Lock implementation within core and edge services. Specifically, to support immutable backups in backup software products like Veeam.

What needs to be done? • Acceptance Criteria

Add the corresponding to GetObjectRetention endpoint on the satellite (the endpoint can be named differently) to respond with the lock information for the specified object version.

Summary

Implementation reference.

Depends on…

• Decide where and make it possible to store per-object metadata for Object Lock #400

Links

• https://docs.aws.amazon.com/AmazonS3/latest/API/API_GetObjectRetention.html
• an easy-to-read and insightful introduction to Object Lock: Using S3 Object Lock