(1) Define CompactionWorkload in avro to allow storing them in instant files.

(2) Split APIs in HoodieRealtimeCompactor to separate generating compaction workload from running compaction

hoodie-client/src/main/java/com/uber/hoodie/config/HoodieCompactionConfig.java

@@ -108,6 +108,7 @@ public class HoodieCompactionConfig extends DefaultHoodieConfig {
       + ".partitions";
   // 500GB of target IO per compaction (both read and write)
   public static final String DEFAULT_TARGET_PARTITIONS_PER_DAYBASED_COMPACTION = String.valueOf(10);
+  public static final String DEFAULT_COMPACTOR_ID = "default";
 
   private HoodieCompactionConfig(Properties props) {
     super(props);