Output plugin kafka - Description for "required_ack" option

Hi,
The description for the "required_ack" is very short, possible values are not described nor explained.
The confluent doc describes well what the "ack" option means, it could be reuse to describe the required_ack value (https://docs.confluent.io/current/installation/configuration/producer-configs.html):

The number of acknowledgments fluentd requires the kafka leader to have received before considering a request complete. This controls the durability of records that are sent. The following settings are allowed:
- _required_ack=0_
If set to zero then fluentd will not wait for any acknowledgment from kafka at all. The record will be immediately considered sent. No guarantee can be made that kafka has received the record in this case, and the retries configuration will not take effect (as fluentd won't generally know of any failures).
- _required_ack=1_
This will mean the kafka leader will write the record to its local log but will respond without awaiting full acknowledgement from all followers. In this case should the kafka leader fail immediately after acknowledging the record but before the followers have replicated it then the record will be lost.
- _required_ack=-1_
This means the kafka leader will wait for the full set of in-sync replicas to acknowledge the record. This guarantees that the record will not be lost as long as at least one in-sync replica remains alive. This is the strongest available guarantee.

Default: -1
Valid Values: [-1, 0, 1]