Update Rally logs track to use new logs index mode

[salvatore-campagna]

Description

After introducing the new index mode logs we would like to update the Rally elastic\logs track to include indexing, storage usage and query latency tests. The idea is to have the new track and its challenges ready soon after introducing the new index mode so to be able to see improvements or, eventually, regressions as soon as we introduce new features. We should rely as much as possible on default settings which are settings we identified to represent typical scenarios. We need to udpate dashboards too so that we are able to spot differences by looking at graphs.

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)

[martijnvg]

Maybe additionally the http_logs can be modified to have an additional challenge for the new index mode?