This series contains a mixed bag of improvements to `scylla sstable dump-data`. These improvements are mostly aimed at making the json output clearer, getting rid of any ambiguities.
Closes#12030
* github.com:scylladb/scylladb:
tools/scylla-sstable: traverse sstables in argument order
tools/scylla-sstable: dump-data docs: s/clustering_fragments/clustering_elements
tools/scylla-sstable: dump-data/json: use Null instead of "<unknown>"
tools/scylla-sstable: dump-data/json: use more uniform format for collections
tools/scylla-sstable: dump-data/json: make cells easier to parse