roachtest: create a roachtest demonstrating read performance during point tombstone buildup

As described in https://github.com/cockroachdb/pebble/issues/918, certain workloads are prone to buildup of point tombstones at the storage layer, which can significantly degrade read latency. This was addressed in https://github.com/cockroachdb/pebble/pull/3790, but we should have a roachtest to demonstrate the performance improvement at the CockroachDB level.

Workloads involving a queue are especially susceptible to this issue. The section titled "CockroachDB Workload" in the comment [here](https://github.com/cockroachdb/pebble/pull/3790#issuecomment-2251439492) describes a queue-based workload where we saw read performance slowly worsen over time as tombstones build up. This could be adapted directly into a roachtest, but it may also be worth investigating other workload types since average latency still only degrades from 1ms -> 7ms in that case before the tombstones are compacted away by previously existing heuristics. We have seen cases where reads can take multiple seconds, e.g. in the liveness range (https://github.com/cockroachdb/cockroach/issues/128968).

Jira issue: CRDB-41649