Support user authentication using Kerberos

[sbernauer]

Description

Closes #285

Missing

• docs
• tests for accessing restserver
• docs on discovery

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 => Copy/pasted from hdfs
- [x] CRD documentation for all fields, following the [style guide](https://docs.stackable.tech/home/nightly/contributor/style-guide).
- [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. Follows the [style guide](https://docs.stackable.tech/home/nightly/contributor/style-guide).
- [x] 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

[sbernauer]

It would be great if someone could review the actual code, docs will follow

[maltesander]

First batch, will continue and test tomorrow!

[sbernauer]

Started https://ci.stackable.tech/view/02%20Operator%20Tests%20(custom)/job/hbase-operator-it-custom/131/

[sbernauer]

Just to be sure: https://ci.stackable.tech/view/02%20Operator%20Tests%20(custom)/job/hbase-operator-it-custom/132

[maltesander]

LGTM!

[sbernauer]

Many thanks for the quick review!