Added support of YDB_FEATURE_FLAGS

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 47.46%. Comparing base (871ddc1) to head (5381b4d).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #328 +/- ## ============================================ + Coverage 47.41% 47.46% +0.04% - Complexity 1739 1743 +4 ============================================ Files 305 305 Lines 12381 12385 +4 Branches 1235 1236 +1 ============================================ + Hits 5871 5878 +7 + Misses 6049 6047 -2 + Partials 461 460 -1 ```

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