New workload: so (StackOverflow flat posts)

[janhoy]

Port the OSB so workload. CC-SA-3.0 Stack Exchange flat question/answer posts. Broad full-text search and faceting on a large, familiar corpus. Lower priority than nested (same source data) but useful as a standalone flat-document workload.

Tasks

• Convert OSB workload using solr-orbit convert-workload
• Define operations: full-text search on title/body, tag faceting, date sort
• Add 1k sample corpus for test-mode
• Check whether any operations belong in common_operations/ rather than this workload

Depends on: #3 (ASF dataset hosting must be resolved before corpus files can be finalised)

References

• OSB workload: https://github.com/opensearch-project/opensearch-benchmark-workloads/tree/main/so
• Creating workloads: https://github.com/apache/solr-orbit/blob/main/CREATE_WORKLOAD_GUIDE.md