[GOBBLIN-2040] Remove the assumption that value of ComparableWatermark has to be comparable (#3935)

* address comments

* use connectionmanager when httpclient is not cloesable

* remove the assumption that value of comparableWatermark has to be comparable

---------

Co-authored-by: Zihan Li <zihli@zihli-mn2.linkedin.biz>

Author: ZihanLi58

gobblin-api/src/main/java/org/apache/gobblin/source/extractor/ComparableWatermark.java

@@ -20,7 +20,7 @@
 /**
  * {@link Watermark} that is also {@link Comparable}.
  */
-public interface ComparableWatermark<V extends Comparable<V>> extends Watermark, Comparable<ComparableWatermark>{
+public interface ComparableWatermark<V> extends Watermark, Comparable<ComparableWatermark>{
 
   V getValue();