Revert "fix: is merge should be False by default (#1701)" (#1706)

This reverts commit da2be57.

jina/drivers/search.py

@@ -47,7 +47,7 @@ class KVSearchDriver(BaseSearchDriver):
             - K is the top-k
     """
 
-    def __init__(self, is_merge: bool = False, *args, **kwargs):
+    def __init__(self, is_merge: bool = True, *args, **kwargs):
         """
 
         :param is_merge: when set to true the retrieved docs are merged into current message using :meth:`MergeFrom`,

tests/integration/level_depth/yaml/index-chunk.yml

@@ -35,5 +35,4 @@ requests:
       - !KVSearchDriver
         with:
           executor: chunkidx
-          is_merge: true
           traversal_paths: ['m']

tests/integration/level_depth/yaml/index-doc.yml

@@ -15,5 +15,4 @@ requests:
       - !KVSearchDriver
         with:
           executor: docIndexer
-          is_merge: true
           traversal_paths: ['m']