Fix N+1 SQL regression in exporting issues to CSV
!50449 (merged) refactored
ExportCsvService
to support both issues and requirements. However, it
introduced an N+1 SQL query when loading labels of the list of issues
that significantly slowed down exporting of many issues.
We bring back the memoization for labels inside the
Issues::ExportCsvService
to avoid this.
Closes #321622 (closed)