Add reference to Kerberos in Kafka input and output documentation (#22342)

Author: kvch

filebeat/docs/inputs/input-kafka.asciidoc

@@ -160,6 +160,14 @@ Kafka rebalance settings:
 *`retry_backoff`*:: How long to wait after an unsuccessful rebalance attempt.
 Defaults to 2s.
 
+===== `kerberos`
+
+beta[]
+
+Configuration options for Kerberos authentication.
+
+See <<configuration-kerberos>> for more information.
+
 [id="{beatname_lc}-input-{type}-common-options"]
 include::../inputs/input-common-options.asciidoc[]
 

libbeat/outputs/kafka/docs/kafka.asciidoc

@@ -294,3 +294,11 @@ Configuration options for SSL parameters like the root CA for Kafka connections.
 `-keyalg RSA` argument to ensure it uses a cipher supported by
 https://github.com/Shopify/sarama/wiki/Frequently-Asked-Questions#why-cant-sarama-connect-to-my-kafka-cluster-using-ssl[Filebeat's Kafka library].
 See <<configuration-ssl>> for more information.
+
+===== `kerberos`
+
+beta[]
+
+Configuration options for Kerberos authentication.
+
+See <<configuration-kerberos>> for more information.