feat: add toString for RowKeyWrapper to ease debugging (#3648)

Author: igorbernstein2

bigtable-client-core-parent/bigtable-hbase/src/main/java/com/google/cloud/bigtable/hbase/util/RowKeyWrapper.java

@@ -66,4 +66,9 @@ private int compare(ByteString key1, ByteString key2) {
  }
  return Integer.compare(key1.size(), key2.size());
  }
+
+ @Override
+ public String toString() {
+ return key.toString();
+ }
 }