Document the snapshot export to S3

[siegfriedweber]

Description

Document the snapshot export to S3

Documents #486

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

# Reviewer
- [x] Documentation added or updated. Follows the [style guide](https://docs.stackable.tech/home/nightly/contributor/docs-style-guide).
- [ ] Changelog updated
- [x] Cargo.toml only contains references to git tags (not specific commits or branches)

# Acceptance
- [x] Feature Tracker has been updated
- [x] Proper release label has been added
- [x] [Roadmap](https://github.com/orgs/stackabletech/projects/25/views/1) has been updated

[lfrancke]

Can you please include a link to the generated nightly docs?

[fhennig]

https://docs.stackable.tech/home/nightly/hbase/usage-guide/snapshot-export