Add javadoc comments for public methods related to KafkaIO redistribute. (#35812)

* Add javadoc comments for public methods related to KafkaIO redistribute.

* Add formatting to javadoc comments

* Add param and return comments

* Run ./gradlew :sdks:java:io:kafka:spotlessApply

Author: tomstepp

sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaIO.java

@@ -1093,19 +1093,55 @@ public Read<K, V> withTopicPartitions(List<TopicPartition> topicPartitions) {
 
     /**
      * Sets redistribute transform that hints to the runner to try to redistribute the work evenly.
+     *
+     * @return an updated {@link Read} transform.
      */
     public Read<K, V> withRedistribute() {
       return toBuilder().setRedistributed(true).build();
     }
 
+    /**
+     * Hints to the runner that it can relax exactly-once processing guarantees, allowing duplicates
+     * in at-least-once processing mode of Kafka inputs.
+     *
+     * <p>Must be used with {@link KafkaIO#withRedistribute()}.
+     *
+     * <p>Not compatible with {@link KafkaIO#withOffsetDeduplication()}.
+     *
+     * @param allowDuplicates specifies whether to allow duplicates.
+     * @return an updated {@link Read} transform.
+     */
     public Read<K, V> withAllowDuplicates(Boolean allowDuplicates) {
       return toBuilder().setAllowDuplicates(allowDuplicates).build();
     }
 
+    /**
+     * Redistributes Kafka messages into a distinct number of keys for processing in subsequent
+     * steps.
+     *
+     * <p>Specifying an explicit number of keys is generally recommended over redistributing into an
+     * unbounded key space.
+     *
+     * <p>Must be used with {@link KafkaIO#withRedistribute()}.
+     *
+     * @param redistributeNumKeys specifies the total number of keys for redistributing inputs.
+     * @return an updated {@link Read} transform.
+     */
     public Read<K, V> withRedistributeNumKeys(int redistributeNumKeys) {
       return toBuilder().setRedistributeNumKeys(redistributeNumKeys).build();
     }
 
+    /**
+     * Hints to the runner to optimize the redistribute by minimizing the amount of data required
+     * for persistence as part of the redistribute operation.
+     *
+     * <p>Must be used with {@link KafkaIO#withRedistribute()}.
+     *
+     * <p>Not compatible with {@link KafkaIO#withAllowDuplicates()}.
+     *
+     * @param offsetDeduplication specifies whether to enable offset-based deduplication.
+     * @return an updated {@link Read} transform.
+     */
     public Read<K, V> withOffsetDeduplication(Boolean offsetDeduplication) {
       return toBuilder().setOffsetDeduplication(offsetDeduplication).build();
     }