Benchmark profiles and multi-turn conversations

[Hugoch]

What does this PR do?

This PR adds:

• a --profile parameter to select a benchmark profile which presets benchmarker relevant options and data file. It makes it easy to launch a benchark for a given use case and have reproducible results.
• the support of multiturn conversations where the full conversation turns are fed back to the model (including previous model response) to simulate chat use cases which will benefit from prefix caching.