Improve performance of updateDataLeaves

Avoid fetching descendants during batchUpdateDataLeaves,
as descendants are not needed:
- Remove prefetch descendants step from getFragmentEntities;
- Explicitly prefetch descendants in operations requiring it;
- Update performance tests (5x faster for batch update).

Issue-ID: CPS-1675
Signed-off-by: danielhanrahan <daniel.hanrahan@est.tech>
Change-Id: I7442a6f799cc0803b3a78f09d1ee53377f24b0b7