[HUDI-2332] Add clustering and compaction in Kafka Connect Sink (#3857)

* [HUDI-2332] Add clustering and compaction in Kafka Connect Sink

* Disable validation check on instant time for compaction and adjust configs

* Add javadocs

* Add clustering and compaction config

* Fix transaction causing missing records in the target table

* Add debugging logs

* Fix kafka offset sync in participant

* Adjust how clustering and compaction are configured in kafka-connect

* Fix clustering strategy

* Remove irrelevant changes from other published PRs

* Update clustering logic and others

* Update README

* Fix test failures

* Fix indentation

* Fix clustering config

* Add JavaCustomColumnsSortPartitioner and make async compaction enabled by default

* Add test for JavaCustomColumnsSortPartitioner

* Add more changes after IDE sync

* Update README with clarification

* Fix clustering logic after rebasing

* Remove unrelated changes

hudi-utilities/src/main/java/org/apache/hudi/utilities/HoodieCompactor.java

@@ -164,7 +164,7 @@ public class HoodieCompactor {
     // Get schema.
     SparkRDDWriteClient client =
         UtilHelpers.createHoodieClient(jsc, cfg.basePath, "", cfg.parallelism, Option.of(cfg.strategyClassName), props);
-    if (cfg.compactionInstantTime == null) {
+    if (StringUtils.isNullOrEmpty(cfg.compactionInstantTime)) {
       throw new IllegalArgumentException("No instant time is provided for scheduling compaction. "
           + "Please specify the compaction instant time by using --instant-time.");
     }