Add config param to specify subdirectory within S3 bucket where backups should be uploaded

What does this MR do?

Addresses Issue #23221 (closed). Currently, there's no way to upload backups to an S3 bucket anywhere besides the root of the bucket. This change adds an option to specify the path within the bucket where your backup files should go. The option simply makes use of Fog's ability to do what we're trying to do here.

Are there points in the code the reviewer needs to double check?

N/A

Why was this MR needed?

Issue #23221 (closed)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• [ x ] Changelog entry added
• [ x ] Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • [ x ] All builds are passing
• [ x ] Conform by the merge request performance guides
• [ x ] Conform by the style guides
• [ x ] Branch has no merge conflicts with master (if it does - rebase it please)
• [ x ] Squashed related commits together

What are the relevant issue numbers?

#23221 (closed)