[#xx] object: Extend PatchRequest.Body with new_split_header field

* This field updates object's split header.

Signed-off-by: Airat Arifullin <aarifullin@yadro.com>

object/service.proto

@@ -887,6 +887,10 @@ message PatchRequest {
     // key, then it just replaces it while merging the lists.
     bool replace_attributes = 3;
 
+    // New split header for the object. This defines how the object will relate
+    // to other objects in a split operation.
+    neo.fs.v2.object.Header.Split new_split_header = 5;
+
     // The patch for the object's payload.
     message Patch {
       // The range of the source object for which the payload is replaced by the