fix: Add orderly shutdown steps to all kuttl tests

[adwk67]

Summary

• Adds a 90-shutdown-kafka.yaml step to all 11 kuttl test suites that gracefully scales down Kafka before kuttl deletes the namespace
• ZK-mode tests (7 suites): patches the CRD to set broker replicas to 0, with a force-delete fallback if pods don't terminate within 120s
• KRaft-mode tests (4 suites): scales brokers to 0 via CRD, deletes the KafkaCluster CR to stop operator reconciliation, then force-deletes controller pods (controllers can't be scaled via CRD due to a "no Kraft controllers found to build ConfigMap" error)
• Sets gracefulShutdownTimeout: 60s in install templates to bound the worst-case shutdown wait (default is 30 minutes)

Problem

During namespace deletion, ZooKeeper/controllers and Kafka brokers are terminated simultaneously. In ZK-mode, Kafka's controlled-shutdown retries ZK connections indefinitely, keeping the process alive for the full terminationGracePeriodSeconds (up to 30 minutes) and blocking namespace deletion well past kuttl's 300s timeout.

Test plan

• Full nightly suite run (26/26 PASS) on Replicated k3s cluster (K8s 1.35.3)

Related: #956

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

[adwk67]

Closing in favour of #956 (and #955) as those PRs are less invasive and thus less prone to masking issues.