[#xx] object: Store EC chunk's parent parent's attributes

In FrostFS we can:
- Split a big object into parts: Object -> Parts
- Split an object into chunks: Object -> Chunks
- Do both: Object -> Parts -> Chunks

And object's attributes are propagated in the following way:
- Object (attributes) -> Parts (no attributes)
- Object (attributes) -> Chunks (attributes)
- Object (attributes) -> Parts (no attributes) -> Chunks (no attributes)

As a result, in a FrostFS node, there's no way to determine the expiration epoch
of an expirable regular object. Now attributes are stored in the following way:
- If a chunk's parent has no parent, store chunk's parent's attributes
- If a chunk's parent has a parent, store chunk's parent's parent's attributes

Signed-off-by: Aleksey Savchuk <a.savchuk@yadro.com>

object/erasurecode/split.go

@@ -33,19 +33,21 @@ func (c *Constructor) Split(obj *objectSDK.Object, key *ecdsa.PrivateKey) ([]*ob
 		chunk.SetPayload(payloadShards[i])
 		chunk.SetPayloadSize(uint64(len(payloadShards[i])))
 
+		attributes := obj.Attributes()
 		var parentSplitParentID *oid.ID
 		if obj.HasParent() {
 			splitParentID, ok := obj.Parent().ID()
 			if ok {
 				parentSplitParentID = &splitParentID
 			}
+			attributes = obj.Parent().Attributes()
 		}
 
 		ecParentInfo := objectSDK.ECParentInfo{
 			ID:            parent,
 			SplitID:       obj.SplitID(),
 			SplitParentID: parentSplitParentID,
-			Attributes:    obj.Attributes(),
+			Attributes:    attributes,
 		}
 
 		ec := objectSDK.NewECHeader(ecParentInfo, uint32(i), uint32(len(payloadShards)), headerShards[i], uint32(len(header)))