GH-3589: Refactor toMessage batch method and fix logging/header issues

[bky373]

Description

• Fixes: Duplicate header processing in BatchMessagingMessageConverter#processRecord() #3589
• Remove duplicate logging and listenerInfo operation that occurs for each record in processRecord().
• And refactor the tasks in toMessage() as follows:
  • addRecordInfo(): Adds information such as type, payload, key, etc. from the record to the given lists.
  • addToConvertedHeaders(): Adds the converted value of record.headers() to convertedHeaders.
  • Extract the value of the KafkaHeaders.LISTENER_INFO key from convertedHeaders, and put it to rawHeaders after the loop ends.
  • If there's no headerMapper, log a message so that users can refer to KafkaHeaders.NATIVE_HEADERS. As there's no need to check boolean logged every time in the loop, the logged variable has been removed, and the check for the existence of headerMapper and natives is now performed only once after the loop ends.

Note

Also, I changed the logging level from DEBUG to WARN when there is no header mapper. INFO might be better, please let me know what you think. -> Sorry, I'll keep DEBUG because it's logged every time the listener poll.

[sobychacko]

Merged via 5fb1562.