PERF-2572 add warmup phase, lower initial/ secondary document count and name each index.

[jimoleary]

There is a patch, but it is being blocked by a compile error.

[apodelko]

Another option may be to run the patch multiple times and see how much the fix helps.

[jimoleary]

Updated the branch with PR comments. Started a new patch.

note: I'm actually going to move the current LLTMixed.yml to LLTMixedWarmup.yml and reinstate the old version before committing. This is for 2 reasons:

1. We want to keep the original workload, so keeping the task name keeps the history. This test will likely be noisy but it does provide a useful signal.
2. I wanted to be able to compare the new workload to the old one.