docs: update kakfa consumer max_batch_bytes config doc

The note text was true for older version Kafka which may return a
partial message in fetch response so consumer would have to feth
again immediately with max_bytes expanded.
Recent Kafka versions always return a complete message.

rel/i18n/emqx_bridge_kafka.hocon

@@ -63,7 +63,10 @@ consumer_offset_commit_interval_seconds.label:
 """Offset Commit Interval"""
 
 consumer_max_batch_bytes.desc:
-"""Set how many bytes to pull from Kafka in each fetch request. Please note that if the configured value is smaller than the message size in Kafka, it may negatively impact the fetch performance."""
+"""Set how many bytes to pull from Kafka in each fetch request.
+Messages are fetched in batches by the consumer, and if the first record batch in the first non-empty
+partition of the fetch is larger than this value, the record batch will still be returned to ensure
+that the consumer can make progress. As such, this is not a absolute maximum. Set `1` for minimal latency."""
 
 consumer_max_batch_bytes.label:
 """Fetch Bytes"""