[OPIK-8175] [BE] perf: skip the dataset item-count scan when a version supplies items_total - #8075

691 tests   - 31   691 ✅  - 31   10m 16s ⏱️ + 1m 26s
 31 suites  -  4     0 💤 ± 0 
 31 files    -  4     0 ❌ ± 0 

Results for commit 5528323. ± Comparison against earlier commit e30a82b.