feat: support producer batching configuration

[freeznet]

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[github-actions]

@freeznet:Thanks for your contribution. For this PR, do we need to update docs?
(The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[jiangpengcheng]

One runner-compatibility issue must be addressed before merge. See the inline finding.

[jiangpengcheng]

[P1] Do not emit batchingSpec without defining a compatible runner baseline.

The repository builds and tests runners from streamnative/sn-platform:3.2.2.1, whose Function.proto does not contain ProducerSpec.batchingSpec. Its Java and Python runners reject unknown JSON fields while parsing --function_details, so setting batchingConfig makes the pod exit before user code starts. The added tests only validate the operator-side proto and cannot catch this incompatibility.

Please add an E2E test using a PIP-401-capable runner and document/enforce the minimum runner version—upstream Pulsar 4.1+—or update the supported runner baseline.