Add operations to cover search fetch performance

[jtibshirani]

The current tracks and operations make sure to exercise common queries and aggregations. However they don't really cover fetching top hits. This is another important aspect of search where it's very possible to introduce a performance regression.

It'd be great to extend some track to exercise search 'fetch' more thoroughly. We could increase the search size to emphasize the importance of fetch performance, and test features like _source loading and the fields option.

[jtibshirani]

Here's an example of the type of PR where it would have been helpful to have these benchmarks: elastic/elasticsearch#77064. We instrumented the search fetch phase with profiling code, and want to guard against a slowdown when profiling is not enabled.