fix: Actually propagate OPA package name

[sbernauer]

Description

Fixes #878

The code should be cleaned up (e.g. use the helper functions on stackable_operator::commons::opa::OpaConfig), but I decided to keep this fix small.

Adopted the kuttl test accordingly

Definition of Done Checklist

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Author

• Changes are OpenShift compatible
• CRD changes approved
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Reviewer

• Code contains useful comments
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• (Integration-)Test cases added
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• Changelog updated
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Acceptance

• Feature Tracker has been updated
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Release notes

Fixed

The operator now utilizes the .spec.clusterConfig.authorization.opa.package property instead of hard-coding the package name to nifi

[maltesander]

Thanks, works.

[maltesander]

LGTM!