source is kafka , not support kdc without ssl

[muziling]

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Describe the bug

source is kafka , connect to kafka with kdc failed without ssl

To Reproduce

run fluentd with below config

Expected behavior

connect kafka success

Your Environment

- Fluentd version:fluentd-1.16.2
- TD Agent version:
- fluent-plugin-kafka version:fluent-plugin-kafka-0.19.2
- ruby-kafka version:ruby-kafka-1.5.0
- Operating system:
- Kernel version:

Your Configuration

fluent.conf: |
    <source>
      @type kafka_group
      # list of seed brokers
      brokers s1.test.com:6667
      principal "kafka/s1.test.com"
      keytab "/etc/kafka.service.keytab"
      topics k8slog
      consumer_group fluentd-k8s
      format json
      sasl_over_ssl false
    </source>

Your Error Log

2023-12-07 08:13:30 +0000 [error]: #0 unexpected error error_class=ArgumentError error="SASL authentication requires that SSL is configured"

### Additional context

_No response_