[kafka] Topic description metadata path mismatch + missing per-topic schema validation

[cagriekin]

Summary (P2 — bug + validation)

Two topic-management issues:

1. description path mismatch: the topics ConfigMap template reads $topic.metadata.description (templates/kafka-topics-configmap.yaml:29), but the documented example shape (tests/values-full-test.yaml) puts description at the top level of each topic. Result: the description is silently dropped from the rendered docs.
2. No per-topic schema validation: values.schema.json does not constrain kafka.topics at all. Nothing catches non-integer partitions, or replicationFactor greater than the broker count (which makes the topic-init job hang/fail at runtime with no pre-flight signal).

Fix

Reconcile the description location (pick top-level or metadata.* and align template + examples). Add a topics schema (partitions/replicationFactor as positive integers, config as a string map). Add a render-time guard for replicationFactor <= broker count.

Related: #59.