feat: Support graceful shutdown

[sbernauer]

Description

Please add a description here. This will become the commit message of the merge request later.

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

# Author
- [x] Changes are OpenShift compatible
- [x] CRD changes approved
- [x] Helm chart can be installed and deployed operator works
- [x] Integration tests passed (for non trivial changes)
- [x] Changes need to be "offline" compatible

# Reviewer
- [x] Code contains useful comments
- [x] (Integration-)Test cases added
- [x] Documentation added or updated
- [ ] 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

[maltesander]

Just some doc nitpicking and changelog. LGTM otherwise.

[sbernauer]

Started https://ci.stackable.tech/view/02%20Operator%20Tests%20(custom)/job/kafka-operator-it-custom/53/

[maltesander]

LGTM if test passes!