Switch to v2 object split scheme

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 9.13462% with 189 lines in your changes missing coverage. Please review.

Project coverage is 26.71%. Comparing base (d6d4636) to head (e016f43). Report is 32 commits behind head on master.

:exclamation: Current head e016f43 differs from pull request most recent head 8328780

Please upload reports for the commit 8328780 to get more accurate results.

Files	Patch %	Lines
api/layer/multipart_upload.go	0.00%	71 Missing :warning:
api/layer/neofs_mock.go	0.00%	36 Missing and 1 partial :warning:
internal/neofs/tree.go	0.00%	30 Missing :warning:
api/data/tree.go	0.00%	16 Missing :warning:
internal/neofs/neofs.go	0.00%	13 Missing :warning:
api/layer/tree_mock.go	0.00%	9 Missing :warning:
api/handler/object_list.go	12.50%	6 Missing and 1 partial :warning:
api/handler/multipart_upload.go	0.00%	4 Missing :warning:
cmd/s3-gw/app_settings.go	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #957 +/- ## ========================================== - Coverage 26.92% 26.71% -0.21% ========================================== Files 87 87 Lines 14129 14246 +117 ========================================== + Hits 3804 3806 +2 - Misses 9903 10017 +114 - Partials 422 423 +1 ```

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