System Performance Benchmarking

Hi! In threads like #738, I see a lot of people trying different hardware and software setups, followed by checking the logs for the `llama_print_timings` output to see performance results. From my (admittedly short) time playing around with my own hardware, I've noticed a lot of inconsistency between runs, making it difficult to evaluate changes. I would suggest an enhancement like an `ollama bench <model>` command, which would set up a suite of example prompts, which would be sequentially or randomly sent to the LLM and the data recorded. This way, we can all have a consistent way of comparing benchmark runs, which would also be excellent for development. Introspecting a running session and just keeping a performance log, separate from stdout, would also be excellent. Is there a way to do this already, maybe through `llama.cpp`? I would be happy to try and implement this with some help 👍 Cheers, Julian