Extend, enhance and regularly cover tombstones handling in SCT workloads

[mykaul]

1. Add mixed insert/update/delete/read workload, not mixed update/read. I don't think cassandra-stress is prepared for that, and I don't think our other tools are either (do they even perform validation on read?)
2. Add correctness check (see above) to ensure there's no data ressurection
3. Performance tests - at least stress testing with many tombstones
4. ICS + TWCS

The focus should be on tombstone_gc=repair, but not exclusively.

[pehala]

We need to extend existing SCT tests to have batchlog writes in the workload - From scylladb/scylladb#20260

[bhalevy]

1. Add mixed insert/update/delete/read workload, not mixed update/read. I don't think cassandra-stress is prepared for that, and I don't think our other tools are either (do they even perform validation on read?)

The deletes mix should contain: partition deletes, single row deletes, and (clustering) range deletions.

Also, add TTL-based expiration to the mix.