fix(benchmarks): make kafka.version optional in Helm template

[k-wall]

Summary

Fixes the kafka.version template rendering to be truly optional, allowing Strimzi to provide a default when the value is not set.

Problem

Commit ed1d43e removed kafka.version from values.yaml to allow Strimzi to default the version. However, the template still unconditionally rendered:

version: {{ .Values.kafka.version }}

When .Values.kafka.version is undefined, this produces version: (empty/null), which Strimzi 1.0.0 rejects with:

spec.kafka.version: Invalid value: "null": spec.kafka.version in body must be of type string: "null"

Solution

Wrap the version field in a Helm conditional:

{{- if .Values.kafka.version }}
version: {{ .Values.kafka.version }}
{{- end }}

• When kafka.version is not set: field is omitted entirely, Strimzi uses its default
• When kafka.version is set: field is rendered normally

Testing

Verified with helm template:

Without kafka.version:

helm template benchmark helm/kroxylicious-benchmark | grep -A 5 "spec:"

Result: version: field is absent ✓

With kafka.version:

helm template benchmark helm/kroxylicious-benchmark --set kafka.version="4.2.0" | grep -A 5 "spec:"

Result: version: 4.2.0 is rendered ✓

Notes

This issue was discovered when testing PR kroxylicious#3887 on a cluster with Strimzi 1.0.0, which has stricter validation than Strimzi 0.51.0 (the version this PR targets).

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