benchmarking: Run benchmarks with non default shard settings

## Description

Currently, our benchmarking doesn't tweak any of the default integration settings or the Elasticsearch settings that would allow more writes to be performed concurrently and increase the event throughput.

I would be interesting to understand what the effect of tuning the `index.number_of_shards` has and what the its scaling properties are, since oftentimes, our customers want more processing power and they just increase the APM Server size, which provides a greater buffer, but in practice, doesn't increase the indexing throughput of Elaticsearch if that is the limiting factor with the default `index.number_of_shards: 1`.

## Related issues

Follow up from #7858