fix: Use PascalCase for metadataManager field in CRD

[sbernauer]

Description

Fixes #1033 in a non-breaking way.

We now accepts (old) lower and (new) PascalCase variants at the same time.
In a future release we might remove the old, deprecated naming, hence we put the issue on the deprecation board.

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

• Changes are OpenShift compatible
• CRD changes approved
• CRD documentation for all fields, following the style guide.
• Helm chart can be installed and deployed operator works
• Integration tests passed (for non trivial changes)
• Changes need to be "offline" compatible
• Links to generated (nightly) docs added
• Release note snippet added

Reviewer

• Code contains useful comments
• Code contains useful logging statements
• (Integration-)Test cases added
• Documentation added or updated. Follows the style guide.
• Changelog updated
• Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

• Feature Tracker has been updated
• Proper release label has been added
• Links to generated (nightly) docs added
• Release note snippet added
• Add type/deprecation label & add to the deprecation schedule
• Add type/experimental label & add to the experimental features tracker

Release notes

Fixed

Previously, spec.clusterConfig.metadataManager was using lowercase values (zookeeper and kraft). Per Kubernetes conventions, we switched them to PascalCase (ZooKeeper and KRaft). The old names are deprecated, but are still accepted for backwards compatibility and may be removed in a future release

[razvan]

thanks

[NickLarsenNZ]

LGTM