[HUDI-476]: Add hudi-examples module (#1151)

add hoodie delta streamer mock source example and dfs source and kafka source examples

Signed-off-by: dengziming <dengziming1993@gmail.com>

add defaultSparkConf utils method

change version of hudi-examples to 0.5.2-SNAPSHOT
change the artifcatId of hudi-spark and hudi-utilities
alter some code to adapt kafka2.0

Update scritps

Add license

hudi-common/src/main/java/org/apache/hudi/common/model/HoodieAvroPayload.java

@@ -67,4 +67,9 @@ public class HoodieAvroPayload implements HoodieRecordPayload<HoodieAvroPayload>
     }
     return Option.of(HoodieAvroUtils.bytesToAvro(recordBytes, schema));
   }
+
+  // for examples
+  public byte[] getRecordBytes() {
+    return recordBytes;
+  }
 }