Set default memory resources for the ZooKeeper quorum

[delthas]

What does this PR do, and why do we need it?

Sets defaults.zookeeperResources in solution/zenkoversion.yaml, alongside the existing defaults.kafkaResources. Without it the quorum pods run BestEffort and the zookeeper image sizes its JVM heap as a percentage of the host memory instead of the container limit (RD-1962 finding).

Which issue does this PR fix?

Fixes ZENKO-5316.

Special notes for your reviewers:

Requires the zenko-operator supporting the field (scality/zenko-operator#624). With an older operator the unknown field is pruned by the CRD, so merging this first is harmless.

Issue: ZENKO-5316

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